Windows 98 freeze.

I have a client running Windows 98 in a 6 user peer to peer network. One of the PC’s, which acts as the email/internet server, completely locks up about once a week. When it locks up a loud, high pitched, screeching noise can be heard from the motherboard speaker. The only way to get the PC out of this state is to hit CTRL-ALT-DEL, which reboots the PC immediately. There doesn’t seem to be a certain application or process that causes this sporadic error?

Any advicewould be much appreciated.