Can think of a few things that might cause this. Best case scenario is that the fan settings are fubar in BIOS - try setting everything to permanently run flat out and retest. If the fan speeds don't drop then that's good news.
Alternatively, it could be a dicky PSU, a bad fan connection on the motherboard or a bad fan. If you are truly disgusted by using stock cooling, which you should be , then replace with something decent and retest. If that doesn't show any improvements then its time to look at your PSU or mobo.
Probably worth seeing exactly how far your fan speeds are dropping when loading the CPU. Use Everest or similar to keep an eye on it. There will be a little natural variation (100rpm or so at full speed).