Problem with PSU??

Bought a Tagan 480W modular PSU from Scan in December. Only just got the rest of the kit to connect it up to, and while the fan is extremely quiet, the PSU itself seems to be making a high-pitched clicking noise. (sounds electrical rather than mechanical)

Any ideas what this might be? Is it broke? It seems to be running absolutely fine. I've got the 12V line split at the moment, as I believe this is the ATX v2 spec. Dunno if that makes any difference.

Not under heavy load - Opty 144, 1 hard drive, 1 DVD burner, 1 x nVidia 6800 GS

Mike