I have a parts express 250W plate amp running an Adire Audio Tempest wired to 4ohms. Anyways, the amp is producing a very bad buzz through the sub (sounds like 60Hz). I've unplugged the amp from the receiver, buzz still there. The amp can have power to it and not buzz, but as soon as I turn he switch to ON, I get the harsh buzz. Also, when I touch the switch the pitch of the buzz changes. What can I do? Could the switch have gone bad? Thanks in advance!