Radio volume went out after a popping sound in the rear. It turns on and I can hear it but very faintly.

If your car has premium sound it will have a power amp in the boot, it is a common problem for this to fail and burn out all 4 door speakers and leave only the little tweeters working. that is why you can just hear it, you can check if this has happend by removing one door panel and check the speaker resistance using a ohm meter. hope this helps.

If power is more than speakers can handle this will happen. If you have a amplifier in the rear than all it is a fuse or a circuit breaker needs to be reset