Easy peasy... you're not looking at 60Hz hum, your cable signal's too hot.
If you just moved into the house (or if you're just taking a close look at your cable for the first time) what's probably happened is some previous owner had the cable come in to a
8 way unpowered splitter so they could watch The Price is Right everywhere in the house including the john... each split of your CATV is about a 4dB loss with a good passive unit... that means you're 12dB down at each of the 8 taps before you even add cable line loss... they called up the CATV provider and complained their picture was snowy, cable guy comes out, realizes their signal's too low at the TV drops and cooks it up 15dB. Next guy comes along, takes the crappy splitter out, replaces it with a better splitter, or one with less taps, and suddenly the signal's so strong you're getting crosstalk from neighbouring channels (appearing as a rolling picture over the program or various other manifestations)... so how do you fix it... call the cable provider? You have a picture, they've done their job, they're not going to tweak every armchair TV guy's signal on their route...
You need an attenuator (we call them pads) P/E has them in
3dB,
6dB and
12dB varieties. How much pad do you need? Who knows... and the equipment to test RF signal strength isn't worth the bucks unless you're a cable company... so buy one of each, they're $2 a crack... and try them in order... they'll give you up to 21dB of attenuation in 3dB increments. If you guessed too high a pad, the picture will be snowy or washed out, like bad antenna reception, if you guessed too low, they problem you have now will still be there.
My $0.02 based on your description, anyway. If the picture is actually more like snow, you're probably too low instead. You can try an
RF amplifier but it's best to not amplify a weak signal, at that point, call the cable company and get them to give you more juice at the pole instead.
For future reference, 60Hz hum is usually a HORIZONTAL band that moves through the picture... anything else is usually signal or interference related.
Bren R.
