That's interesting. Because ground loop isolators tend to reduce high frequency response, and thus I usually try to avoid using them, I would have thought a subwoofer would have been the perfect place to use them since high frequencies are not needed. I'm assuming these were opto-isolators?

I'm interested in whether it's genuinely a ground loop, or if it's a bad amp, or potentially even a bad subwoofer. This statement in your earlier post intrigues me:



Can you describe this in more detail? What exactly do you mean by "tried another source on the amp"?

While we're here, how is the receiver output wired to the subwoofer amp input? Also, how sure are you of the ohms of the subwoofer, since the sub amp probably requires different wiring for 4ohms or 8ohms.