I stumbled upon this utility from Maxtor for adjusting the acoustic settings on Maxtor HDD's.
Acoustic Management adjusts the speed of the head seeks, reducing the ambient sound level during the normal operation of Maxtor hard drives. This does not affect sound levels for power on operations. The performance of the drive is affected when Acoustic Management is enabled.
I installed it on my Maxtor drive, a 40G DiamondMax Plus D740X. It appears that these drives come from the factory with the acoustic management set to its midrange setting, on but fast. Adjusting it to its quietest setting made my drive marginally quieter. My drive was already nearly silent, being suspended, sandwiched, and sidesinked, so the adjustment may make a bigger impact in a drive that is installed normally. The performance hit from the adjustment seems to be about nil, less the 2% according to my benchmarks in PCMark2002.