Many are willing to help you, but you must offer much more info.
Full build spec and age of system is a start. First make sure it is not a fan. The PSU's fan
can be blocked with a non-conductive probe, then the rig booted. The rest can be stopped
with a finger as suggested.
Are any of the caps bulged or venting.? When you press on the toroidal coils does the sound
change.? (Google images) Have any heat sinks been removed from board chips in a rough
manner.? (CPU excluded) If it's a P4 board you may have to change it out. It does not
happen often but they are known to be talkative.
...Galvanized