Interesting series of noise-related problems. Sorry to hear things aren't all peachy with the MG.

The battery icon appearing is covered here. The crackling might be related to one of the things in that list, too.

The pop may be the diode thing, but it also might be all tied into the same problem (crackling and battery icon). Cleary something is not right with the power or the wiring that supplies your stereo system, and it should be checked out.

Maybe the fluid is just low in your battery? (Not kidding, check it, assuming you have the kind of battery that needs fluid)