OP stands for "original person" i.e. the person who started the thread.
I've got a 36gb Raptor and its the noisiest thing i've ever heard in a PC, i've got a Coolermaster Cosmos case which stores its HDD's in caddies that are sound proofed with rubber gromets to isolate the drives from the case to stop vibration and you can still hear the Raptor when the head is shooting across the disk. It sounds a little like hail falling on a tin roof when doing the random access test in HDTACH.
Now the Samsung Spinpoint 501LJ 500GB £65 drive i recently put in is practically inaudible in this case even when running HDTACH to benchmark the drive. The Raptor you can hear from the other side of my flat ( I'm not exaggerating) when doing the same benchmark, the Spinpoint you can only hear if the room is quiet and you stick your ear a foot or two away from the case. The Spinpoint benches at 90mb a sec down to 45mb at its slowest, the Raptor goes from 65mb a sec down to 45mb a sec.