Hi mrmazzer, I had exactly the same problem on my 4200, and as suggested above it was a short on one of the door speakers. It only takes a couple of minutes to remove the securing screws and drop the speaker out, as soon as I did this the sound came back on again. The short circuit on the wiring connection to the speaker was very apparent, and easily rectified with some good insulation tape. There is also a fuse not mentioned in the handbook and it will kill the sound if open circuit. It is a 10 Amp fuse fitted in the back of the NIT unit itself. But, learn by my mistake, and go for the easy speaker option first, remove the speakers and inspect the connections. At least now I know how to remove the NIT unit, but that was unnecessary, it was the speaker short circuit !! Cheers.