My 99 A4 2.8 Avant QM with the Bose system has recently developed a nasty habit of "popping" loudly from the left speakers (both front and rear) when I go over bumps. When this happens, there is momentarily almost no signal to the left speakers (in other words, very low volume) and then the signal comes back up. The pop occurs regardless of the volume setting on the head unit - even with the volume all the way down, I still get a loud pop. Of course, if the head power is off, there's no noise. I'm figuring there's a loose power connection to the left channel of the amp - but I don't know where to look. The problem is intermittent enough that the dealer hasn't been able to find it in two tries, although they have replaced the head unit. Any ideas where I should start looking would be appreciated - maybe starting with where they hide the amp(s) in this car? I searched for info in the FAQs and archive, but may not be asking the right questions... so if this has already been disucssed, please just tell me where to look.