Thanks all for the replies. Let me try to answer each of you.
First, to FullRangeMan. Thanks for explaining what you meant by inverting the outlet pins. I should have realized that outlip was a typo.
All my power cable cables are three prong. I'm in Massachusetts, so I'm on US current. On the system that's picking up the radio station I had a four outlet wall box installed. I believe it's going into one circuit. I have a lot of equipment, so I have four powerstrips, each with surge protection, going into this four outlet box. I don't know the frequency the buzzing or radio station is coming in at. There is no cable box connected to either of my two systems. These are both strictly stereo music only systems. I guess my next step will be to start disconnecting pieces of equipment, one by one, and also try separating cables, one by one. Also, I should insure that any pieces that require grounding are all being grounded to the same ground post.
Thanks again,
George M