XM antenna did not fix the problem. On a recent trip, it was whistling a lot. Stopped at the first Lowe's, bought a roll of painters tape and followed odonnell747's idea and started taping things off till it stopped. Just like odonnell747, I believe it is my center light assembly. I need for it to warm up some so I can be sure this is it. Mine only seems to whistles when the temperature is above 60 degrees. Sorry it has been a while, but the temperature is a factor now.