That's a really old PSU with low efficiency (it's not 80+ gold as advertised, it's not near that at all). According to thermaltake's website, the fan spins from 1525rpm to 2400rpm. Both speeds are clearly audible for a 120mm fan. I recommend you to search for a 80+ certified PSU (80+ bronze or better) from a reputable brand like seasonic, evga, corsair, and buy it. The power supply is one of the most important component to improve the stability and life span of your computer, don't cheap out on them!
Personally, I would not dare to use that Thermaltake TR2 power supply. For one thing is it very old and the second thing is the very poor reputation it has for being a quality power supply. Can you get your $$ back and get a much better power supply? (a low quality psu can take out your entire system, do not chance that)
your probably using the maximum output and that's why the fan is running so fast I would get something in the 600-800W range and not necessary new ,