I had a similar experience with my Seagate 7200.7 drive. I was using it in a fanless system, so any sounds the HD made would be really obvious. While overall the idle sounds were very quiet, they had a decent amount of high frequencies. I wouldn't exactly say it annoyed me, but it was very obvious. Btw, i'm also very alert of high frequency sounds - I can "hear" when a TV is turned on from several rooms away, and i'm not talking about its volume. I think its the photon gun that i'm hearing. Anyway...
I returned the drive and bought a Samsung one instead. My initial impressions were very positive. Besides it being a cooler drive, the drive was also much quieter. Although its maybe a *tad* louder on idle compared to the Seagate, there are much less high frequencies on the Samsung drive. Seeks are no contest - the Samsung drive is a ton quieter. I can barely hear them above the idle noise. The Seagate sounded like a loud rattling sound in comparison.
Keep in mind that I'm running a fanless system, so any noise the HD makes would be noticeable. However, both would probably be inaudible in a normal system with a power supply fan, HSF, video card, etc.