loud hard drive

hi all. i have a dual 2gb G5 with 2 hdds. ever since i got leopard this year i've noticed that the hard drives seem to spool reaLLY LOUD! i've tried setting the processor to automatic to see if that helps (no difference) i'm not running time machine so it isn't that and i don't think its related to usage as if i put it into sleep over night it seems to come out of sleep mode and do it halfway through the night and actually wake me up (even though it's downstairs). if anyones ever had to reinstall/repair it's louder than the disk search/repair thing (can't remember what it's called). anyone got any ideas on how to make it quieter? it only seems to have happened since i got leopard . oh and i have 4gig of ram so i'm pretty sure it's not performance related.

thanks in advance

neil