Serious hum problem. Help

Long time no post...

I just moved, and hooked up my system to my housemate's television. The TV gets its cable signal directly from outside- ie through an RF cable, no cable box. Whenever I plug the RF cable into the TV, the hum is awful. Changing the input on the amp or switching cables out makes no difference. I bought a new, shielding RF cable, but it didn't help at all.

Any ideas?

Thanks!