Faulty HU-803 CD changer - any ideas?

I have had an S60 2.0T SE since Jan '02, and been generally pleased with the car. However, since mid-May a problem has developed with the stereo system and I wondered if anyone had encountered the same or could offer an educated guess.

The stereo performed perfectly from new until driving in torrential rain one morning in May. An intermittent crackling (like a loose connection to a speaker) developed on the left channel only, which occurred only under acceleration and driving uphill. The problem only affected the CD player, not the radio.

On my first visit to the dealer to have the problem investigated a faulty radio was diagnosed (the fact that the problem occured in heavy rain seems to have been a coincidence), a replacement was ordered and fitted a few days later. Immediately on picking the car up following the repair the problem recurred (did they not test-drive it?), and to cut a long story short, I am stuck at the moment with a non-funtioning CD player in a car that has been back five times to the dealer to have the problem investigated and corrected. As time has passed, the defect has become more severe, occuring under most driving conditions, but still only affecting the left channel. On a couple of occasions I have managed to park with the left channel totally dead - this allowed me to play about a bit and I found that with the balance full left (to cut out the right channel) and the volume VERY high music was JUST audible from the left speakers. I don't know whether this was actually the left channel or just cross-talk from the right.

I would be very grateful to hear any suggestions from anyone who has either had a similar problem or who knows anything about car stereo systems and has an idea what might be going on. The car is due back with the dealer again in a couple of weeks for more "tinkering", but I get the feeling they are now making it up as they go along!

Many thanks in anticipation!!!

Tony.