Here is a strange situation. When the telephone line is connected to my HR21-100 AND the LED pot lights in the TV room are on, there is a hum (60 Hz) on the telephone line. If I disconnect phone line from the HR21-100, there is no hum, regardless of whether the lights are on. If I turn off the lights, there is no hum regardless of whether the HR21 is connected to the phone line. The hum is only present when the HR21 is connected to the phone line and the lights are on. I thought that the phone line itself might be acting as an antenna to pick up RF interference from the lights, but if I leave the line connected at the wall and disconnect it from the HR21, the hum goes away. I have tried using phone cables of different lengths in an attempt to find a length that is not a harmonic of the interference, but that had no effect on the hum. I have tried routing the phone line through a surge protector and without the surge protector with no change. If it was a grounding problem with the HR21, I would expect the hum to be independent of whether the lights were on. The lights and the HR21 are on different electrical circuits, but both are from the same service panel and both are grounded properly. The only thing I have not yet tried is using a shielded phone cable that is designed for use with ADSL modems, but since the hum is not present when the existing cable is attached to the wall but not to the HR21, I doubt this will solve the problem. Does anyone have any ideas?