I logged in to upvote this story because I encountered the same problem on a military communications system once (!) There was an interaction between the system beep() function and message processing throughput. If a large number of alerts ever queued up, communications slowed to a crawl as the CPU spent all its time going "beeeeeeep...beeeeeeep...beeeeeeep..." for a few minutes. Moving the mouse caused a rapid-fire "bebebebebebebebebebebeeep" as the buffers flushed and throughput returned to normal.