Well the only way to rule it out. Is to remove it from the circuit. To be on the safe side, remove the radio fuse and the audio amp fuse. Or just unplug the amp. There are 3 or 4 connectors on the amp, don't worry you can't mix them. They can only go back into their original hole. The amp is located on the drivers side in the trunk. Just pull back the carpet lining and you'll see the vertical installed amp. If you want to do the fuses, they are located in the drivers side fuse box that is under the rear seat.
With that said, there has been a problem that I've seen on here a couple times. Both ha a battery drain issue, new or old battery. And I recall their issue being the RIM, rear integration module. That fuse is located in the passengers side under the rear seat. So try the amp, radio then the RIM. give it a few days between each fuse removal.