Sounds like a whiney fan,can you hear it right at the back of your case ??,,does the noise stop when you momentarily stop the fan ??..
Other than the fan there are no moving parts in a psu [but you already know that,eh
So,,,if it is not the fan then something is really out of whack,maybe you should deal with OCZ directly,I have a StealthXStream 600 and it is very quiet...:)