I've just fitted my Alpine ida-X305 head unit into my 2001 S3. The car has Bose and had the Symphony head unit. The Alpine powers up and works fine, all the speakers are working and I'm pretty sure the tupperware sub is as well. However, I get a really loud THUD through all the speakers when I either turn the volume down to 0 or change source on the head unit. It doesn't seem to happen at any other time. I'm using the same Autoleads adaptors that I used to install the Alpine in my pre-facelift S3 which was non-BOSE, could this be the problem? Any help would be appreciated, I don't want to keep trying things because I'm sure the thudding won't do the speakers any good.