dealer replaced radio, still doesn't work

Any advice would be appreciated:
I have a 1998 528i. The radio started going dead, even the time
didn't show in the display area. Off/on switch did nothing.
Periodically the time will reappear, then the radio works for
a while. First dealer trip - radio is bad, ordered and replaced
($$$) and the same thing happened immediately. Second dealer trip
- new radio is defective, ordered another. Third dealer trip to
install second new radio, say need help from BMW, BMW knows about it,
pickup my car until they get information.
Any ideas? Maybe there's a short somewhere and it never was a
radio problem? I have kept the car serviced/inspections done.
Do you think I will ever hear back from the dealer? Any experience
when the dealer says waiting on help from BMW?