Well I thought i would share my thoughts on the subject since a lot of us are looking for a solution to the drone issue. I put the SLP PowerFlo system on tonight and the install went as expected. When i started the car it sounded great a deep rumble not to loud for a "family car" but just enough to get some attition from anyone looking to challenge the "family car". So I went for a ride and thats then things stopped going a expected. from 1200 to 1800 RPM the drone is horrible. At highway speeds when the DOD activates there is a very deep tone thats irritating when listening to the radio. I was on the road for about an hour and ended up with a headach. I wanted this system for two reasons, I liked the look of the tips and the claim of no drone. I will be calling SLP on monday to see if maybe I just got a defective system and if not they will be getting there product back.

Thanks for the update and info. Much appreciated.

hmm, good luck

Sounds like my experience with Pypes.

Sorry to hear about your experience (no pun intended). I will have to post mine, when my Magnaflow 16795s get here.

Again, drone is very subjective in that what is acceptable, or in fact desired, to one set of ears, may be intolerable to another set!

Unfortunately the only reliable "drone meters" are your own ears.

try driving a Chevy pickup with a straight piped 350 as a daily driver, then you will find out what drone really is.

Me too. I installed my Power Flo exhaust yesterday. If you like the quietness of your stock exhaust it is not for you. On the hwy the AFM drone is very loud. Also mild resonance at 2,000 rpms in 6th gear. IMHO SLP could have done a better job at this exhaust.

damn I was leaning on either this or pypes!! Back to the drawing boards... :(

damn I was leaning on either this or pypes!! Back to the drawing boards... :(
Yeah, no kidding. Not sure what I'm going to do myself. I've had a good email exchange with Borla and they're fully aware and experienced the drone on our cars when they were in developement for a cat-back for the G8 GT's. Their response is they would be misleading people if they said there's no drone at all on the current Borla cat-back on the market. Having said that, they've minimized it enough that they're confident I would be happy with the result seeing that I made clear to them I've personally experienced the drone issue on my car with a failed attempt at a competitors muffler axle-back setup. I was trying to do it on a budget and obviously failed at this approach.

do you think dynamat'ing the whole trunk would kill the drone?

do you think dynamat'ing the whole trunk would kill the drone?

If you're considering this. Ask the specific company that supplies or makes the material since they're sound specialists. I wouldn't know if that would work or not since where do you stop with the sound deadening material? Trunk only or the entire interior? I doubt the trunk only would solve the problem since the exhuast is running down the middle of the car. That's my opinion only.

Yeah, no kidding. Not sure what I'm going to do myself. I've had a good email exchange with Borla and they're fully aware and experienced the drone on our cars when they were in developement for a cat-back for the G8 GT's. Their response is they would be misleading people if they said there's no drone at all on the current Borla cat-back on the market. Having said that, they've minimized it enough that they're confident I would be happy with the result seeing that I made clear to them I've personally experienced the drone issue on my car with a failed attempt at a competitors muffler axle-back setup. I was trying to do it on a budget and obviously failed at this approach.

I am really leaning on Borla as the sound is just mean!! I do like the SLP pro-flows as it will be my second choice.

Drone will most likely happen with ANY exhaust set-up. On my Acura CL-S I had Comptech exhaust on it and it also had a drone during cruising RPM's. Bottom line is you either you hate it or you like it!! :driving:

If one of you guys wants to get rid of it let me know.

I want to try something just to see how the drone is, I'm not too old but I'm not sure I could handle there "loudmouth" no muffler deal.

OK I spent a lot of my weekend tinkering with these things doing anything I could think of that would absorb or reflect the drone with no success. The problem is the fact that it is low frequency noise and to stop it you would need a large amount of dense material. After that i jumped online and began searching any post on any sites that discussed this issue. It seems that a lot of the aftermarket kits have this drone problem and that some have found solutions although I do not think they will work for us. I still plan on calling SLP in the morning and ask that anyone else that is dissatisfied with theirs call also. The more people that call the better our chances our that the will remedy the issue.

I also found this post that sums up all the questions about exhaust drone

There is a lot of talk about exhaust drone on this forum and others. I know I've read one person claiming they have no exhaust drone and another with the same exhaust claiming they have considerable drone. The subject of drone is not SUBJECTIVE as some may claim. It's either there or it isn't. There is drone and there is exhaust SOUND. They are two different things. If a certain make/model of muffler or catback is causing drone for one person it also will cause it for another on the same type of vehicle unless there is some type of problem with installation that is causing an exhaust leak. Since it is obvious that some people to not understand or realize what exhaust drone is, they then don't think they have any.

Some people seem to think drone is only something you experience at highway speeds above 50 mph. It's not. If you are getting drone at high speeds on the highway, your also getting it at lower speeds around town. Speed doesn't matter, it's the RPM range that matters. It's in the 1500-2000 RPM range that drone usually happens when the engine is under a load and that can be at a variety of speeds depending on what particular gear the transmission happens to be in at the time.

I just joined the forum today and this topic hits home, one where i needed to hear others' experiences. I installed the Magnaflow Axel Back mufflers on my 09 GT. Results: 'same as you guys' disappointments. Sweet idle; not bad when running on all eight cyls but really annoying, loud droan and vibrations felt in 4-cyl mode where 70mph in cruise control is miserable. The problem appears mostly caused by resonant vibrations occurring in the trunk of the GT. There is no sound deadening material at all under the trim carpeting lining the trunk, At idle, you place a hand on the trunk floor and vibration is felt. I'm beginning to explore sound deadening materials for the trunk. Quiet Car may have an answer to be able to live with some performance exhaust on the GT.

Somebody on "the other forum" posted that they applied dynomat to their trunk and it seemed to cut the drone by about 40-50%. Something to look into.

I just put a Magnaflow 16795 on my car and the drone @ 1800 rpm under load is brutal. I can live with the AFM drone, but the drone at this RPM is so bad that it overpowers the stereo no matter how loud its cranked.

Needless to say I'm also looking for a solution; I too am considering adding a bunch of dynamat to the trunk floor. I believe this will make a difference, I pulled my spare tire cover out this weekend since I'm fabricating a sub enclosure for the spare tire well, and with the cover off the drone is even worse. I have to assume if removing sound deadening material makes it worse, adding some should make it more liveable. On top of the dynamat, I'll have a bunch of 5/8" MDF in the spare tire well so this should insulate very well.

I have a feeling the spare tire well acts like a drum, applifying the resonance from the exhaust (making that deep boomy sound thats so annoying). Next time your in your trunk, make a fist and rap on the spare tire cover, you'll hear a deep boom almost like someone kicking a bass drum. I think with the mufflers being on either side of the well, the frequency from the exhaust is bouncing off the well which gets amplified by the empty space.

As a last resort, I notice SLP makes 2.5" resonators that are only 4" in overall diameter. These would be easy to add in to the magnaflow after the X pipe, and would hopefully quell some of the resonance.

I also found this post that sums up all the questions about exhaust drone

There is a lot of talk about exhaust drone on this forum and others. I know I've read one person claiming they have no exhaust drone and another with the same exhaust claiming they have considerable drone. The subject of drone is not SUBJECTIVE as some may claim. It's either there or it isn't. There is drone and there is exhaust SOUND. They are two different things. If a certain make/model of muffler or catback is causing drone for one person it also will cause it for another on the same type of vehicle unless there is some type of problem with installation that is causing an exhaust leak. Since it is obvious that some people to not understand or realize what exhaust drone is, they then don't think they have any.

Some people seem to think drone is only something you experience at highway speeds above 50 mph. It's not. If you are getting drone at high speeds on the highway, your also getting it at lower speeds around town. Speed doesn't matter, it's the RPM range that matters. It's in the 1500-2000 RPM range that drone usually happens when the engine is under a load and that can be at a variety of speeds depending on what particular gear the transmission happens to be in at the time.

I agree that drone is an acoustical phenomenon, which is measurable. The subjective part I'm talking about is how a particular person reacts to it.

Even though the drone is at whatever db it is, and at whatever frequency it is, some people will be annoyed more than others.

I agree with you also, in that drone occurs a specific RPM or RPM range, it's just unfortunate that for us, that cruising speed is in the dreaded "drone range".

Still, one person's unbearable, intolerable drone, is one person's bad-ass exhaust music.

Hey, as one person said, if you want quiet, leave it stock!! Evidently GM knows how to prevent drone.

Called SLP this morning and they said that this was the first time that they had this issue with our car and that he was going to get with his R&D people to figure this out. Also I would not waste time with dynamat. Over the weekend I dynamated the entire trunk ,spray rubberized the underside of the trunk and filled the spare tire well with fiberglass insulation. It may have helped with about a 5% reduction in drone. The best solution is to get someone to make quality exhaust.

Very good new postings, Adrian thru Woody. Thanks guys. I've Googled & explored every advertised source for sound & vibration control i could find. I want to retain the original lay of all the trunk coverings. For me mats (like Dynomat) appear to be too thick to do that. I'm awaiting feedback from Quiet Car (check out http://www.quietcar.net/). Technically their material appears to be a credible solution to fully cover the areas - sides, corners as well as flat surfaces. Also in my good deal (an 09 MGM w/all options except the Sport Pkg which i did not want the summer only tires) the dealer very reluctantly exchanged my GT's dull, 'fugly' 18 inchers with those from a new G8 (6-pac). These the Code N87, bright split-spoke wheels (the best looking G8 OEM wheels, IMHO) and he threw in a spare compact wheel. Still awaiting the compact tire from Tire Rack and my backordered, tire well stuff (jack, tools, mounting block, etc). I think when i land and tie-down the entire spare tire assembly in the well, that ought to quiet the drumming from there.

What? I cant hear ****!! LOL

Just playin, drone is there but I guess my tolerance is a little more than others because mine isnt a daily driver. I knew there would be drone but didnt care. It is personal preference as to how much drone you can stand or how long.

Here is a thought that just crossed my mind while reading about the possible causes. I noticed while installing my Power flos that they sit extremely close to the heat shield. There is the possibility that when installed, they could touch the shield, which in turn is next to the hollow bass drum we call the spare tire well. Any vibration would be amplified by that well. Kind of like a constant drumming, if you will. I don't know that it would be the sole cause, but it sure as hell can't be helping the issue. I need to check to see if mine is actually touching or not. I don't believe that I am experiencing the same sound as others. I don't consider that "tone" annoying at all. Maybe thats just me, though.

If you find a deal on some foam pillows, just stuff the trunk with them!

Sorry for the slow response my boss had me in Florida for some training all week. Anyway SLP called me on Wednesday and they said the they had been looking into the problem and could not find anything wrong. But like any good company would do, they told me to send them my mufflers (shipped at their expense) to see if there might be a problem with mine. This is the first time that I have ordered anything through SLP and to see that they care about their products performance after the sale says a lot about them.
I also wanted to tell anyone that might not know that if your drone is getting louder as the car warms up you might be able to fix part of the problem. As the exhaust warms up the pipes will actually get longer due to expansion. If your muffler is slid to far into the hanger it will begin to push against the metal on the hanger support making the sound even louder. If your not sure if you have this problem take you car for a spin make sure that it is nice and hot, pull over (someplace safe) and take a look but don't wait to long as the exhaust will begin to cool quickly.