yeah when I first got my WD1200JB drives they were dead silent... then after about 9 months they started to make a high pitched whining sound. Working or idle that sound was present. The seek noises never got lod but the whine was pretty bad. Reminded me of when I had an all scsi system.
I got a couple enclosures designed to silence noisy HDs and put them inside them. The enclosures made the drives get really hot, heh especially since I had no case fans (didn't need them before). The high pitched whine could even be heard when the drives were INSIDE the enclosures, thats how bad it was, but it was a lot more bearable than before.
after about 2-3 months of the WDs baking inside the enclosures... the sound stopped, weird. Also I was very impressed they did not bake to death. I installed some fans recently and now, incredibly, the drives seem to stay quite cool in their enclosures. I dare not take them out because I'm scared they will start making noises again, but for now they are dead silent again.
WD drives have pretty good performance, but they need to work on their noise levels