I finally found the water leak in the cargo area of my X5. I just replaced my 3rd radio too. Everyone should check this to avoid a costly repair.
The lower tailgate has 3 drain plugs on the bottom inside edge. You have to flip up the black panel that covers the bottom egde of the door. Pull the plugs out and clean them. Mine were clogged with gunk. When i pulled them water gushed out. When the water gets to a certain level it channels thru the rubber electrical wiring plug and right into the lower cargo area under the spare tire. Then the battery well eventually fills up and ruins the radio, park, distance module, tow package module, and level ride module. It's a 5 minute job to clean these out and replace them. There are also 2 drains on the upper hatch to clean. Hopefully this helps someone else save some $$ and grey hair.

09-11-01
NEVER FORGET