new power supply makinbg a noise, should i worry

hey guys. Im a bit new at this pc building thing, just having done my first major installs today(Power supply and Vid card) so any help would be great.

I ordered an Ultra Power supply from zipzoomfly, mostly because i didnt feel like spending $100+ for a 500watt. Install seemed to go fine, and the PC boots up with no problem. However, the PS is making a sort of whirring noise. It almost sounds like it has some dust in it or something, but i just put it in this afternoon.

It doesnt seem to run that hot, and the noise is not even noticeable unless you put your ear right to it.(most of the time) I added in an extra fan to help get some air flow to the area, but the noise persists. With the fan, you can even hear it, but i know its there and dont want to ignoret. Did i get a defective unit? if i did, id want to send it back ASAP. any help would really be appreciated.

Thisis the PS i have, in case that would help anyone.