Are you ready for this? Aprox 1yr ago this started. When the engine is running, and the vehicle is facing the garage, I can not close or open the garage door. If I back into the street and face away from the house, the door will open and close fine. Have replaced remotes and batteries.I do know that the receiver and remote works on 312mhz and something in the computor operates at 312mhz. The vehicle runs great and has never popped any codes. I exhausted GM tech and service bulletins and GM could not come up with an answer. Same with the door co. The dealer said they could do nothing without a popped code. I have tried other sites with no luck so far. No accessories have been added and nothing has been altered on this vehicle. I can detect a little interferance in the radio sometimes. Also at random times everything works ok. My wife has an 03 blazer with the same engine and she has never had this problem. I also have a remote inside the house and if the engine is running it will not work either. Do you have ANY ideas or suggestions???