Glad you solved your problem.
I had similar RF issues with my USB keyboard and mouse.
One thing that helped was wrapping the entire length of the USB keyboard and mouse cords with a thick layer of aluminum foil (from the kitchen), and then covering the foil with black electrical tape -- just to hold the foil in-place. The cables are much thicker now (and it looks horrendous), but it does work.
Did you have to ground the foil, or did you leave it floating?