How can I stop my amp from buzzing?

My amp keeps making a loud humming noise. I'm not sure if it's coming through my guitar pickups (I have a Fender Strat), or my amp (Marshall MG50). However, I noticed when the TV is on in the living room and I'm playing in my bedroom it's worse than when the TV is off. These types of things are definitely affecting it, but what can I do about it??