I recently acquired a cMP 4,1 (now flashed to 5,1) and I'm hot-rodding the crap out of it. I was wondering about replacing the fans. There's nothing wrong with them, they're just louder than I like. Particularly the expansion slot fan. It'll crank up to around 2000RPM for (what I can tell) no good reason, and then slow down again, sometimes as low as 800RPM, but usually setting around 1300-1400RPM. I was wondering if any old PWM 4-pin (92mm?) fan could be plugged into that fan's header, or if I was limited only to Apple's fan. I have taken the fan out and inspected it, it looks like it'll come out of the assembly, though I haven't actually tried. The other fans all seem fine, so I don't think it's temperature related. The temps in HWMonitor look fine, they don't spin up above the minimum 600RPM (or 800RPM for the one inside the heatsink).