Try this. Power down, remove the side cover, start up. Did the beep stop?
I looked at past beeping problems on C-Net and also on Google but I can't find the situation I have. Once exactly at 3 minute intervals my computer gives a short (1 second) beep. Everything works fine so at first I ignored it but I know something is wrong and if possible I would like to fix it before I have a disaster. My Bios is Phoenix and when I checked beep codes there is nothing listed for 1 beep every 3 seconds. My HDD temp is 100 degrees F which is normal for my computer. I would appreciate it if anyone has any ideas which might explain and cure this beep. My profile lists computer info if needed.