The plastic thing seems to either be an impact barrier if you get hit in the door (like Funkster said) or some kind of weighted resonator to make the door sound more Mercedes like when you slam it closed. Pony- it doesnt seem to be attached to the glass regulator, I dont think its part of that system. Its interesting that it seems to only be screwed to the inner door and the bottom or outerdoor side seem to have foam on them. Why would it only be attached on one side and move around so much? I think its designed to move around when the door slams to absorb resonation or to keep the inner door from vibrating. I think the two screws I have that are rusted to **** are letting it move too much that its hitting the metal bottom of the door, or there is a third attachment point I cant see thats rusted thru.
I'm sure its rust that caused the problems. And its bothering me that nobody else has had this problems (at least I cant find it on the board). And I know why.
I've had the car 10 years (from new) and it was only last year I learned there are actually water drains at the bottoms of the door. I used to get a ton of water in the doors after a big rain and could hear it sloshing around while I drove and I had to leave the door open for hours with stick stuff like pencils or pens wedged under the door seal and the water would slowly drip out of the pins holding the seal in. Back in 2010 ish when the cars were new the consensus on the board was there were no drains and the water wasnt supposed to get it. I did the RTV around the door gasket trick. I sealed the holes at the top of the door. Every 10 rainstorms, one of my doors would hold water. There were a few guys saying there should be drains at the bottom of the door, and some guys drilled holes in the metal, but most people said they were wrong. When I looked at the bottom of the doors I saw some black tabs that were filled with what looked like OEM sealant. So this went on for years of my trying to seal the doors more and it happened less often. I think the thing that helped the most was I moved and my new location I wasnt parking under a tree anymore.
Over a year ago I took one of my doors apart because I couldnt take the water anymore (I was going to drill holes in the bottom of the doors) and I found a mulch like mud at the bottom. When I cleaned it out and I was looking at those sealed tabs from the inside of the door, I realized they ARE drains and mine were just filled with years of ground up dirt and mulchified leaves. I laid on my back under each door with a garden hose and shot water up into those tabs and could see them all clear out, and the water I shot up in the easily drained out of the cleared tabs. I felt like an ass for dealing with this problem for years when it was my drains clogged for years. Sigh. So now IMO the window seals are not designed to be water tight, just to keep 95% of the water out. And the 5% that gets thru is meant to stay behind the plastic sheet in the doors and the water is meant to drain out of the bottom.
Anyhoo, I used to get a ton of water built up in this very door, passenger rear. So thats where the rusted screws came from. Any why this plastic thing is not making a ton of noise.
Now that I have that foam under it, I think its supplementing the foam that exists on the plastic thing and there is no noise. I think I'm going to leave it like that a few weeks and see if the foam moves. If it stays put I'll put the door back together and hope it holds. If the noise comes back or my window gets jammed I know where to look first. Then I'll probably drill out the two rusted screws and see if I can remove the whole plastic thing. Will be curious to see if the door slam sounds totally different with it removed.
I hate being the first person with a problem.