You are getting a ground loop from your crapy cable tv company. You will have a hard time convincing them that is there fault. If you want a cheep solution, you can get some 75om to 300om converts and reverse them. In other words, go to radio shack, get 2 75-300ohm converters. One that has the 75-300 with leads and the other that has the 75-300 that just has the screws on the 300 ohm side. Take the leads on the 300ohm side and connect them to the 300 ohm side of the one with the screws. This will leave you with a 75-75 converter. Since these converters are just transformers there will be no grounding problems and you will not see any reception loss. Good Luck