Split From https://www.bleepingcomputer.com/forums/t/619766/shrill-inconsistent-buzzing-in-desktop - Hamluis.
I've got the same/similar issue driving me crazy! I think I've isolated it to a Seagate 2TB hdd I installed a year ago. System is on a separate 1TB hdd so I unhooked the 2TB hdd and no sound but the mount hardware and all seem very tight so I can't figure it out. It's like a resonance frequency sets up randomly, whether it's under load or just idling. Goes from faint buzzing sound like a piece of stretched cellophane w/a strong airflow across it, starting barely audible to a definitely irritating volume that can't be ignored. I've run SeaTools tests w/no issues found. Banging on the side of the Dell case sometimes lowers or stops it for a while so it's got to be something to do w/the mount.
I did figure out an interesting way to isolate the origin of the sound which is an old school method used be mechanics to isolate the origin of engine noises. I'ts a bit risky to use in a PC but I was desperate. Using a med/long screwdriver (old hard plastic handle type) w/the handle part pressed to your ear, very carefully touch the blade end to suspected areas of the case (never any part of or onto a circuit board!!!) outside first, then if your brave w/steady hands inside parts of the case and it will definitely get distinctly louder when you touch it to the source of the noise. Good Luck.
Edited by hamluis, 19 April 2017 - 11:00 AM.