Hey,
I am having rattles in the back, it's the little plastic vent under the back windshield.
I put a folded up rag right now, is there anything I can do?

I play my music somewhat low. 15,

------:---l--- Bass
------:---l--- Treble
------:---l--- Subwoofer
------l------ Center

It rattles only in that spot, does anybody else have this problem?
If yes, do you guys know how to fix it?

I tried getting to it from the trunk, but the walls are in the way... not much I can do.
I just shoved a folded rag above the plastic vent, and it cancels the vibration a little bit, so it's not hitting the glass as the sub bumps.

 

dynamat the whole back piece?

 

I know exactly what you're talking about and I actually fixed that problem this past weekend. Basically what you have to do is go into the trunk, pull down the carpet covering from the top and you will expose the metal sheet and be able to see the bottom of the speakers. Keep in mind, while you're doing all this keep the radio on so you can clearly hear the rattling. You will see some holes in the metal and what you want to do is press up through the holes and you'll be able to see that plastic vent piece move up against the window. You'll see that the rattling stops once you do this. What I did was bought some felt tape sheets from Home Depot and cut them so they fit in the gaps and push that vent piece flush up against the window like it should be. I know this might sound like a bitch to do but believe me it was VERY easy and I'm not a very handy person. This totally eliminated the rattling sound that I've been dealing with for over 3 years now with my '04 TL. I even brought it to the dealer for service twice for that problem (1st time - NTF (no trouble found), 2nd time they replaced the entired back deck, the rattle was gone for about 2 weeks then came back). Try this fix and you won't regret it. I'll try and post some pics soon of what I'm talking about.