I have a 2004 Lincoln LS v8 with the THX Navigation system. Recently there has a been a buzzing sound coming from the speakers when the car is running and you can see wavy lines in the navigation screen. Everything on the head unit functions fine, volume up down, tuning, gps everything checks out ok. When you turn the volume up the sound stays the same so you can drown it out and not hear it but when you power off the unit by pushing the volume button you can still hear the buzzing. The buzzing does not go up or down when you accelerate, its the same tone. I have been told it could be a ground, took it to a friend/tech and all grounds were securely fastened with nothing being loose. I disconnected the rear deck amp and didnt change anything, checked fuses and its all good. I have noticed that when i go out to my car in the morning after the car has been sitting overnight the buzzing will not come on till after i start the car, also when you i park and turn the key to the engine off position the buzzing will still be there but it will time out after 10-15mins, of course opening the car door will kill the audio system without the keys in the ignition in the acc postion. Has anyone heard or had a problem like this before and can offer a solution? I think its something thats running in the background thats causing the interference, i just want to troubleshoot as much as possible before having to pay a dealership money to investigate the problem.