Circuit split within panel
Check that the receptacles are wired correctly and that the hot and neutrals aren't crossed. As far as diagram the only this I see odd about this is that right circuit the neutral and ground are connected to the same bus. They should be connected like that the circuit on the left. Since the two busses are eventually connected its not dangerous but it may cause a small ground loop and maybe causing the audio hum.

Also I assume you're plugging in a powered speaker. If the audio source is plugged into a different circuit especially if the circuit is the other phase improper grounding can cause a hum.

Let us know what resolved the problem for you.