Xoutpost.com - sound problems

Hi all!

I’m having a very annoying peculiar problem with the sound system in my X5 E53 2001. Every so often the sound switches off completely for no good reason - no CD music, no radio, no talking Sat Nav lady. Everything else looks OK – the computer screen works, you can change CD tracks even though you can’t hear anything, SAT NAV works but not talking. I noticed that if I switch the engine off and on again, everything gets back to normal. Sometimes switching to another CD track helps as well and sometimes the sound comes back in 20-30 minutes without me having to do anything. The BMW garage says that the only way to fix the problem is to replace the whole system for a small price of £570, in other words they can’t be asked to troubleshoot this problem
A year ago I upgraded my MKIII to v28 SW not sure if it’s related but I guess I should mention that

Any thoughts on DIY troubleshooting would be much appreciated!