I'm using a PA amp on a DIY subwoofer and I am getting a ground hum in both the sub and speakers. The PA amp is grounded and the reciever is not which seems to be the problem. I tried the PA amp on an extension cord that eliminates the ground and it sounds fine, hum dissappears. Is it ok to run it like this? Seems like it would be a better idea to ground my reciever then to "unground" my amp. Can I do this? Why are recievers not grounded anyway?