Cheers gents.

Will try cleaning out the fan first and if it persisits I'll pop the sucker apart and have a look at the caps. I'll post pics if I'm not sure.

The PSU is a Chieftec 360W (don't know the exact model) it came with the case a Chieftec Dragon Medium Tower (in loverly blue).

I'll do it tonight if I've got time, I'm putting up coving tonight and I've got some plastering to do but after that if she'll let me finish early. I really hate DIY