Beeping T42

[fschwep]

My T42 has this weird symptom: sometimes it beeps incessantly. It's a regular beeping, not a series of shorter and longer beeps like most error codes. While it beeps, the machine just continues working - a few times I did not even notice for a while as I had a pair of headphones hooked up, lying on the desk, and the sound was too muted. So it must be coming from the speaker/sound-out system. When I restart Windows, usually it goes away.
Screen is OK, keyboard works, everything seems to be functioning, but this is a bit unnerving.
It sounds similar to the beeping alarm associated with an empty battery, when the machine is about to put itself into standby or hibernation. But it occurs while it is hooked to the AC grid by way of a minidock. Battery is new, recently replaced (it also beeped occasionally before the battery was replaced). Mobo was replaced about 16 months ago. It's a 2373 FWG, 40 GB harddisk, 1 GB RAM. I'm also running Centrino Hardware Control with modest downvolting of the CPU.
Anybody who recognizes this?