Unexplained System Sound

[Sceptic Tanker]

Last week my cabinet started making this noise. (Sound warning)

http://vocaroo.com/i/s06O4JWRFPn2

It started happening randomly. Usually gets worse under load.

I can't figure out what it is, but I have my suspicions that it's the PSU.

CONFIG:
Corsair VS 550 (is it a bad choice)
Gigabyte GA 78LMT USB 3 mobile
AMD FX 6300
Kingston HyperX Fury 8GB DDR3 1866

 

[CountMike]

Sounds like a screeching fan.