Shut down the comp. Carefully block the fan from rotating, use something non-conductive. Boot the rig. No more rattle=bad fan. If it's under warrenty, RMA it. If not replace the PSU or change out the fan. If you choose to replace the fan, DO NOT install an under-rated fan. Install a ball bearing fan with the same spec, a good fan. Like a NMB, NIDEC, Delta or Sunnon. Don't use a cheap sleeved bearing fan. That fan lives in a world of heat, it's not a case fan.
Depending on the PSU, some fans use a two pin plug, others have their wires soldered inplace. You might have to cut, splice, solder and heatshrink.
Google, replacing PSU fan. Many tutorials will come up.
...Galvanized