I got my 2nd A4 last Thursday and you are right the neighbors probably think I'm nuts also. But then who cares when you can have 2 great cars to drive. My 2nd A4 was under $25K so I don't think I'm being too extravagant. I am amazed at all the changes from my 98.5. Enjoy both of your cars I know I am.
Roy M 98.5 2.8q tip & 99.5 1.8Tqm

Just finished installing BA Pro 5 with MB quart adapters in the front doors. Ended up with terrible distortions in the range 80Hz - 200Hz coming from vapor barrier.

Initially I thought my head unit limits signal or even gets unstable. Well I got the Prosonus Studio reference Disk CD (pure tones, sweeps etc.) and a scope. Took the panel off and measured the signal at the driver. The head unit does in fact limit but it is stable and the limiting occurs at much higher levels than needed to generate that ugly sound from vapor barrier. I pulled it away and the vibration sound went away (well maybe 90% the other 10% comes from the grille).

Did anyone solve this problem before ? I want to keep stock appearance if at all possible. The only idea that comes to my mind is cutting vapor barrier liner completely around the speaker but this would expose it to elements.

I did apply a lot of silicon cement to the driver magnet and to the door panel around the driver to hold liner in place but it did not help much.

Any help will be gretly appreciated,
Vlad N.