I bought my 2000 A4 1.8TQM just under 2 years ago and heard a rattling sound coming from the driver's side rear woofer. I brought it by a local stereo shop, and the guy said my speaker was blown and that I'd have to take it to Audi to have it fixed since you can't buy new Bose speakers aftermarket. Being the noob that I was to Audi's (i still am a noob, really don't know sh*t about how to work on them), I took it to the Audi stealership and ended up spending over $2000 on minor repairs, including $250 for a new Bose speaker, not including the $150/hr labor charge of installing it. Recently the same speaker began rattling again, and I couldn't understand how it could have blown after having for such a short period of time whenIdo not bump my stereo. After doing some research ona purchasing a used bose speaker and installing it myself, I found out that it is a common issue with Bose speakers to have the glue on the dust cap of the speaker to come undone. I guess Bose does a poor job of glueing them on, maybe tosell more speakers because people think they are blown. I found this DIY
http://www.audiworld.com/tech/elec58.shtmlfor removing and installing rear speakers, which explained how to remove the rear panel to gain access to the rear woofers. Upon disassembling my back seat and inspecting the woofer, I discovered that the dust cap of the woofer had indeed began to seperate from the the speaker. I bought some krazy glue, glued that sucker back on with an excessive amount of glue to make sure it doesn't come undone again, and added some to the other speaker just incase it decided to detach itself also. Speaker sounds great again when the bass hits, and the only money I had to spend was $2 on a little bottle of krazy glue. Hope this helps anyone that may have the same issue. So if you think you have a blown bose speaker anywhere in your audi, make sure it's not just a loose dust cap, because it will end up saving you alot of money if it is. Below is a general diagram of a speaker, showing where the dust cap is located.
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