I've got a fairly loud hum coming out of my Gibson GSS50. I flick the amp on and it kinda pops then it hums. The hum doesn't change no matter how loud or soft I turn the volume. It's also in all the inputs both channel 1 and 2 (there are 2 inputs for each). What could be causing this? Could it be a grounding issue? How do you ground an amp better.