I have a Thermaltake Element V tower with a Xion 850w Bronze PSU. After installing the PSU, plugging in the cables, and turning the computer on, the fan on the PSU starts making a clicking sound. The PSU is firmly in place and nothing appears to be sticking in the fan either from the PSU or the case. I know the sound is coming from the PSU's fan and not another fan. Could it be a defect in the manufacturing of either the case or the fan, or is it something I'm just overlooking.
Xion is a tier 4 or 5(not recommended) psu on this list.http://www.eggxpert.com/forums/thread/323050.aspx
You might consider returniing it in favor of a higher quality unit.
You have covered the bases by verifying that nothing is interfering with the fan.