PC Power & cooling has a great Tech Support Site (see 800 #) - I have 2 of their PSU's. I don't know what could be wrong with yours, but call them - they will support the PSU 100% (so far, they have mine)
Well, now that you mention it, my thermaltake 500W PSU also drops air inside the case. I read on the instructions on the box that it's supposed to do that but it doesnt make much sense, does it? I looked in the PSU and it looks like its divided into two piecies with a transparent plastic. It has only one 12cm fan and it says on the box something like "it recycles the air and drops cool air in the box" but that air is NOT cool!! Damn, I have to look into it myself now!!
so i called pc power & cooling and talked to one of the techs there about the issue i was having...
he asked me some questions about the PSU fan's orientation etc, and seemed satisfied that it was installed correctly to expel air from the case. he asked me about the other fans in my case, i have 2x120mm, one in front at bottom and one in back directly underneath the PSU and in line with the fan on my zalman cps9500. he had me boot up the pc with the rear case fan unhooked and sure enough, the PSU fan began blow air out of the case, albeit weakly. evidently it was just being overpowered by the other fans in my case, but according to the tech it should ramp up and do a better job moving air while under load (i had only examined it while idle thus far). I'm going to give my PC a work out now and see what happens.
The fan should change RPM's as the PSU heats up. My 750 does. Even though its RPM change is almost un-noticeable. Only reason I can even say it does, is because I have used it on a bench built computer where there were no other case fans around and you could slightly hear it doing it but mainly you could just feel the air. PC P&C make some of the best PSU's on the market I wouldn't worry at ALL about it if the Tech said you were fine. Just enjoy your PSU.