question about hard drive noise

[danda821]

I just install a FUJITSU 5400 80G hard drive into my thinkpads. It is quiet for reading and writing access. But in a quiet a room at normal sitting position I can clearly hear the disk rotation sound (like a low level fan noise). Though this noise is much lower than Hitachi 7K100 80G.

I don't know if this is normal for a hard drive with two platters. The Hitachi 5K100 40G which has only one platter is very quiet. I can not hear the rotation sound even in a very quiet room.