Radio Frequency signals are in the air. They're everywhere. Whether or not they are strong enough to be picked up and amplified by your guitar pickups usually depends on your proximity to their source (the tower). If you live in the shadow of a broadcast tower you'd need a lead lined room to avoid it.
Sometimes, they can come and go depending on atmospheric conditions, so if your lucky, it might only be an occasional problem.
I doubt that filtering your power lines will address this problem.
You might be able to minimize the efffect just by changing where you stand in the room, or the direction you are facing. Your guitar is an antenna attached directly to an amplifier. Make sure the pickups,pots, bridge etc. are properly grounded. Make sure you're using a good quality cable with a good shield to the amp. Try moving the amp itself. Also many guitars have some magnetic sheilding in the pickup cavity or on the back of the pickguard. It's like tinfoil, also with a ground wire attached to it. Try a different guitar for troubleshooting purposes. Once you find the source, then you'll know where to concentrate your efforts.
Twist