the 250mhz cpu has a known defect in which it freezes up and emits a
loud hideous screech until you move the mouse, touch a key, etc. you can
google in these groups for info and stories.
it only occurs on the 250mhz 2mb cache indigo2 cpu however. your issue
must be different, can you explain it in any more detail or give background
on what is going on when it happens.
Not trying to rehash anything, I just hope this maybe helps a few people out of some potential confusion.