Can't find thread on NAV with HK stereo problem. Help!

I have got a 2004 325xi with NAV and HK. The CD player sounds fine, but the radio's stereo sounds sometimes fades away and then later fixes itself. I know I read a couple of threads here in the past, maybe 6 months ago, on this very problem but I can't find it now. I brought my car in for its 15k service and naturally the dealer knows nothing about this problem. I want to find the thread to find out how others have resolved this problem. I believe one fester had contacted BMW NA. Any leads would be appreciated.