My first thought is grounding. What type of antenna are you using?
Does the tuner have a 3 prong plug, if so try lifting the ground and also disconnect the antenna when you have it in the system and see if you can isolate the problem. Just a though.
Does the tuner have a 3 prong plug, if so try lifting the ground and also disconnect the antenna when you have it in the system and see if you can isolate the problem. Just a though.