Gidday there Curt,
Thanks for your thoughts. [Linked Image]
I know it's not my HDD, it makes a rumbling sound when it bursts into life and only does this every once in a while.
The CPU fan is as quiet as a mouse.
I'm leaning more towards the PSU fan causing all the noise, it's started to make a heck of a racket when I first switch the computer on, in fact not un-like having a horde of angry bees inside the case. [Linked Image]
But after the computer has been on for a minute or so, the noise goes away and I'm left with a high pitched tone as I mentioned above.
The PSU is a 400W Enermax and I can't say I've had any problems with it up until this came along.
Wierd, if you ask me. [Linked Image]