Strange resonating sound in T61

[Kurtismonger2]

My friend just got a brand new T61 which I setup and configured for him. In the time I spent with it over two days it was fine but he now reports that it is sometimes making a resonating sound which sounds like speaker feedback. He said it sounds like when you rub your finger on the edge of a crystal wine glass and goes from low to high volume. He can't tell if the sound is coming from the speakers. It does it whether the Thinkpad is on his lap on on a table. I also had him make sure there were no other devices nearby and there were no CD's in the drive. It doesn't seem to matter what he's doing on the computer it will just make the sound intermittently.
Anybody got any ideas?