Hi! I've just bought a '99 S80 T6 and the amplifier under the front passenger seat was broken. I've purchased a used one from eBay and replaced it. The amplifier works very good and the sound is powerful enough but there is a distortion in the background even if I turned down the volume. And when I start the engine that distortion turns into an unbearable noise. I have searched for every possible reason (grounding as well) but couldn't find anything wrong. Is there anyone who had the same problem or have an idea about the solution of this? Thanks in advance.

 

I'd check the cabling to the head unit and consider swapping out the head itself as the problem could be in the pre-amp.