If you have a TV
by, 05-07-2012 at 05:14 PM (1852 Views)
You probably need this:
(Click the image for Amazon.com link).
I had a reasonably minor but audible hum in my subwoofer, and I noticed it went away when I detached the cable from my TV. The TV power was turned off, as was my receiver. (Not just standby, but off). Nevertheless, there was a ground loop from the cable to my TV to my connecting HDMI cable to my receiver to my 0.1 LFE input on my sub. I put this in to isolate the incoming cable, and it worked flawlessly.
If there is any potential (pun intended) interaction or connectivity between your TV cable and anything else, or even if you care about your TV signal, this is worth $16. My cable is properly grounded, but this condition still was present.
If you have an HDMI going from your mac mini to your TV or receiver, etc, it may indirectly suffer from this as well.