I install home theater equipment for a living and have seen this problem quite frequently, it is called a ground loop. It is caused from your cable not having a proper ground and using your television as the path of least resistance. There are a few reasons for this problem:
1. Your cable isn't grounded to your houses electrical ground, which is solved by going to any Home Depot or Radio Shack and getting a grounding terminal and connecting it to either your electrical service or your cold water ground.
2. If that doesn't fix it, another cause is the components are farther away from a good groung than your tv is, and the distortion is finding an easier path through your tv to ground. A solution is to have a circuit ran to the outlet your tv is plugged into and tied into the same cicuit that your equipment is. This makes the path to ground easier through your equipment than your tv because it is farther away.
3. Another way that may fix it is getting a good surge suppressor that conditions the power and has a coaxial input this is a very good idea either way. There is also a devise that you can plug your cables into that will eliminate the problem also but I am not sure on the cost so if you google ground loops I'm sure you will find even more solutions.