My 2001 740i has developed cracking noise which seems to be emanating from the rear right speaker.

The sequence of events with the stereo/speakers started about 3 weeks ago with a hum from the left rear speaker as soon as the car was started (the radio did not need to be on). Again, the feedback/hum seemed to be isolated to only the left, rear speaker.

After about 1 week the hum/feedback went away.

The problem since is when I turn on the radio there is a different sound, more of a crackling sound coming from the right, rear speaker.

Interestingly, when i start the car, you can hear an "electronic" type noise or blip from the speaker.

I had car into mechanic for another issue with my battery draining and he determined that water had gotten into rear where nav unit, stereo and amp are located. He said it was dry but it was apparent that water had infiltrated the area.

I have since be told that the amp is likely culprit of crackling noise -- so is it possible to swap the amp from 1999 740i to my 2001 740i? Is this pretty straightforward swap??

Thanks for any thoughts.