Hi, I purchased a 525i, 2005 model, no nav. system, regular radio system, since I purchased the car the radio makes poping noises, and soung goes and comes, also happens with a cd, and with the door open chime, I replaced the MPM, but that did not fix the problem, I just noticed that if the engine is off, and I turn the radio on in the ACC position on the ignition, the radio problem is gone , chime sounds ok etc. So the problem presents itself when the engine is running....any ideas what to look for now? Thanks!

 

Sounds like a bad ground.. but I can't help you much further.