Before you do what I wrote above, Radio Shack has "Ferrite Cores". You can install these on each piece of coax and also on the AC wire going into the boxes...
http://www.radioshack.com/product/in...ductId=2103222
Sometimes putting a couple on works but one on each piece of Coax and on the AC wires to the boxes. This is a cheaper fix that may work.
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