It seems to depend on the mounting more than anything- we use Seagates exclusively for non-server machines here at work (manufacturing company in the UK), and the same drive will sound different in different machines.
For instance, the 400Gb 7200.8 free

evaluation sample from Seagate was silent on a desk, audible in a mini-micro tower, and fairly noisy in a BTX case
Still, they're quieter than most. The only other disks that are quieter are the Samsungs, and I don't rate them.