Audio Systems: 1999 BMW 323i Stock Head Unit Problem, player acts, 1999 bmw 323i

Question
I am having a problem with my 1999 BMW 323i Head unit.  At first the problem started on rainy or damp days.  There was a crackling and the sound would just go away.  This problem went on for a while and finally there is no sound coming from the head unit.  It does power up, I can see the stations, I can scan the stations and it stops on the stations I know and the CD player acts as normal.  Everything is ok but there is no sound.  One of the rear speakers has a small box next to it that may some sort of amp.  I have checked and replaced the two fuses that are for the radio (7 and 41).  I purchased the same radio from ebay and installed it and have the same results.

Answer
The symptom you describe sounds more like a wiring problem than anything else.  I would trace all of the wires to the speakers looking for cracked insulation or frayed wires.  Given that it started when there was rain suggests that the water was shorting one of the wires.
Dan