Question Random crackling/snapping noise coming from computer even when it's turned off

[Sipan9000]

So I've noticed recently that there is a cracking or snapping noise coming from my computer, this happens when it's on or off and quite rare and completely random. I never noticed anything like this until I rebuild my new setup but kept the same case and I've had it for about 6 months and am just now noticing this noise. At first I thought it was nothing but I've been noticing it more often now and I'm beginning to worry, anybody experienced anything like this before?

 

[13thmonkey]

unplug it from the wall.

What PSU is it?