I have the same problem as you. And the additional problem of having the PC in the livingroom, where I am torturing my daughter and girlfriend with the noise :-(
Anyway, when I bought my pc, the already gave me a more expensive fan, because "the got so many people complaining about the noise". That fan was a Thermaltake Volcano. http://www.thermaltake.com/products/heatsink/v7.htm But it is still way to noisy for me. I replaced it by a Zalman. http://www.zalmantech.com/CNPS-5100CU.htm Noise did reduce, though certainly not as much as expected from the salestalk, and not as much as I hoped. And temperature gets pretty high, but I have been told that this is likely because of the mainboard, an ASUS A7V 266E. I am no overclocker, but even with underclocking I need to have the fan running rather high to keep temperatures reasonable. I also replaced the fan in the power supply, which did make some difference, but still not enough. The last thing I will try is replacing the fans with Verax Silencers or Verax Cair dB, but they are hard to find here (Barcelona) All in all, I am pretty annoyed with the whole thing. I certainly regret having bought an AMD Athlon and a ASUS mainboard. I have no experience with Pentiums and other mainboards, but as I understand they don't run as hot. If I would buy my computer knowing all this, I probably would by a PowerMac. Maarten
