if my computer has been on (for say 24+ hours) the cpu will chatter when i move my mouse. it sounds like an old school 8080 through 80386 chip computer thinking and about as loud as a Pentium 4. it only seems to trigger on certain actions like moving the mouse, having a selection box active in paint.net, watching a video. random actions, can be all at once or only one thing at a time.
had all fans turned off while testing it, temps ok, no noticeable functional issues, sound was coming from center of motherboard (where the cpu is located). been known to occur with two different video cards installed.
problem not persistent after reboot, returns after long periods of time at random intervals. been testing over months