I want to get set up with a system and I am a bit confused. I have heard other systems and the rear will vibrate and make terrible rattling noise. I want to put a couple 12's in but what are your guys comments? Experience with systems in the A4?

the trunk, rear deck (top & bottom), trunk lid and you'll be fine. Between Mark P, Vorsicht, myself & others, you won't have any rattling if you dampen correctly. BTW, I'm running 600W to 2 JL 10 W3's, no rattling whatsoever!

but you don't here it on the inside if you are playing the subs loud enough to rattle the plate...otherwise the trunk is pretty tight...i currently have 2 vega 124's and only run one cuz 2 is just too much

rattles BAD. I put 2 layers fo dynamat on the inside of the trunck lid but it doesn't help a whole lot. Its not that it just shakes and makes noise, the whole this flexes when the bass hits. Can't do anything about in unless you reinforce the inside of the lid with braces and that is impossible on my 96, don't know about later models tho. Also, gas cap rattles before truck does. I haven't figured out what it is vibrating against to try to stop it.