When the vehicle is off and stereo is off the speakers are making loud popping and banging noises all the time over the last week? when the vehicle is running and stereo on no popping noises
This can be tricky; there are several things that might cause this 'phantom' problem. You did not state if you have an alarm system. The alarm may be tied into your speakers and/or linked to the stereo itself. I would not initially suspect a ground issue since the stereo works well while powered. I would suspect a power feed issue. This can be tested by removing the fuse for the stereo and seeing if the issue continues.If the problem stops, the source may be internal to the stereo and you may need to get an aftermarket stereo - or pull the fuse every time you stop ( sucky solution, I know!) . I think this may be an issue resolved by a reputable stereo shop. Possibly a strategically placed Diode may solve the problem - a hands on diagnostic is certainly called for. You did not mention if the problem decreases or stops overnight. I would think this can cause your battery to drain over an extended period of time - and ruin the speakers too, if they're not affected already. I would try contacting the Dealer first and, as this problem has gone unresolved for so long, see if you can get them to replace the stereo or at the least pay the stereo shop to fix it.
best of luck and thanks for using Fixya!!