[steiny93]

faced a similar issue (although it was low freq hum) turned out to be coming from the catv line

interesting is that in my scenario there was a surge-suppressor inline which included the catv protection but it didn't work

i diagnoised it by removing all connections then adding them 1 at a time until we discovered the issue

 

[steiny93]

try unhooking stuff until it goes away, then when you find the source try moving the wires that are connected to that source

i believe the rule of thumb is 1ft separation for parallel runs and the rest of the crosses be at 90 degrees.