HP D530 SFF: cpu upgrade & fan noise

So I was upgrading some older equipment, these d530's came w/ a 2.8ghz, 533mhz bus pIV cpu, well I upgraded a couple of them to a 3.2ghz 800mhz cpu.  Dispite putting new heat sink compound, blowing out the CPU fan, and upgrading the bios, the machines would often sound like a Boeing 747 during times of high cpu usage.  I found several posts on the subject, no real answers, most suggestions were stuff I already tried.  What I did stumble on, was that in the bios there is a setting for changing the cpu fan idle speed.  I moved it up to 4, the highest level.  This does make the machine more noisey, because the fan is spinning faster all the time, however it doesn't kick into hyper-speed nearly as often.