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Discussion Starter #1
I've noticed a strange noise sometimes after parking my car. After reversing into a spot (although I can't say it's limited to that), I can sometimes hear a rapid, dull thumping sound coming from near the rear of the car. It sounds like something slowly spinning down, and it can take upwards of a minute to stop. By the end, it's "thumping" less than once per second. Has anyone else heard something like this? My first thought was something in the diff, but it seems to be working fine (even when spinning the tires), no strange noises while driving, and I can't imaging that there could be a spinning mass that would take that long to spin down.

It's odd. Any thoughts?
 

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That usually signifies something like gas sloshing around, which sometimes sounds like a thump. Spinning, though..... maybe the pump?

Pretty much everything else is stopped once the car stops; especially if it is under the car.

Maybe this sound is coming from a different direction? Having somebody else back up into a spot while you listen from outside the car would help.
 

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Discussion Starter #3
It's definitely not fuel sloshing around. I've heard that many times, but this is much different and definitely sounds like a rotating mass spinning down. I'm looking into a possible correlation, though, after noticing that it did it with under a quarter tank of gas, but didn't after I filled up tonight. Maybe the pump, but I didn't think it would have enough spinning inertia to keep going for than long after shutting it off. At any rate, it's strange. I'm also going to have to confirm next time I hear it that it's not coming from the sub in my trunk...
 

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There is a test the car is commanded to run after the car is shut off. It says it would run that test no more than 2 times per day. Its called the EONV test (engine off natural vacuum test) Its looking for any signs of a small leak condition. The fuel tank changes internal pressure due to getting hotter as you drive along. It continues to get even a little hotter for a little while after engine shutdown occurs (due to escaping exhaust heat near the tank). The self testing is looking for pressure changes that exceed (higher or lower) than the system expects to see, and *could* last for several minutes on occasion. I think the EVAP vent valve (an even the purge valve) can or are cycled open an close at various rates an total times to perform the test *if necessary* to complete the testing. *If* this is so, maybe those sounds you hear are a result of that testing. Kinda sounds like a far out last ditch possibility. Or if you reactivated that BAP system, maybe its got a mind of its own, or not.
 

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Discussion Starter #6

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Discussion Starter #8
Well a simple test. Pull the fuse for the bass amp for a few days and see if it goes away.
The trouble is that it's not consistent. I think I just need to wait for it to happen again, then pop the trunk and put my hand on the sub to see if it's doing the pulsing.
 

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Its the evap system. Mine does it too. No need for concern.
 

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Discussion Starter #10
If that's the case, I'm rather disappointed in myself that it took me ten years to notice it...
 

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There are several requirements that must happen *before* the car will run that test. Pretty much all of them will happen each time you have a run cycle (like total run time, fuel level still in the tank, total miles/kilometers covered etc) The one requirement that *has* to happen to get that test to run at all, is that the car had to have been off for at least 17 or more hours from its last run cycle. If the car is most always restarted before reaching that no run time period, the test will not happen. I've never had the luck of hearing it either. So I'm thinking that whenever it does run that test, you would have had to be standing in the right location, probably with very little surrounding noise, to have a shot of hearing it in the first place. An it can run that test very quickly, or take up to 40 minutes if necessary to complete the test, based on how the temps an pressures in the tank are changing.
 

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There are several requirements that must happen *before* the car will run that test. Pretty much all of them will happen each time you have a run cycle (like total run time, fuel level still in the tank, total miles/kilometers covered etc) The one requirement that *has* to happen to get that test to run at all, is that the car had to have been off for at least 17 or more hours from its last run cycle. If the car is most always restarted before reaching that no run time period, the test will not happen. I've never had the luck of hearing it either. So I'm thinking that whenever it does run that test, you would have had to be standing in the right location, probably with very little surrounding noise, to have a shot of hearing it in the first place. An it can run that test very quickly, or take up to 40 minutes if necessary to complete the test, based on how the temps an pressures in the tank are changing.
I guess this is why I hear it almost weekly. My car will sit in the garage for about 24 hours before its ran again. The time I usually hear it is when I get back fro the gym, pull in the garage, turn car off and watch a youtube video or two before I even get out and back in the house lol
 
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