It sounds like something trying to restart. These fans should run on 12vdc. Generally motors use 12v and logic circuits use 5v. It would be good to know if any other voltages can be read at the PS connector on the motherboard.
Well my computer was custom built but not by me and i just have no clue how to fix my problem. when i shutdown my computer it makes all the normal shutdown noises and then my fans get a little quiet like they are about to turn off then about 3 seconds later they go full speed and just never stops. i have to turn the whole power supply off to get them to stop. the computer appears to be shutdown but its loud cause of the fans... and all fans are on the cpu fan the side fans and the power supply fan. any ideas why this happened or how i can fix it.

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