The silentdrive did wonders on the electrostatic whine, which is what I was more interested in eliminating. (Seeks became inaudible, too.) I have never heard of WD drives being listed with Seagates as quiet, but I have heard people saying Maxtor SEs are only slightly noisier. The Maxtors are just now (as Seagates have been using) fluid bearings, which greatly decreases both the electrostatic and seek noise. I have not heard of WDs using fluid bearings.
For comparison, I do have a Maxtor 60 gig fluid bearing drive in my Tivo, and it is slightly audible (i.e., if the room is quiet I can hear that it's on). The Seagate 'cuda IVs that I have are inaudible. I can just barely hear them when they're *seeking*. YMMV depending on the noise of the other components in your case - I have a feeling people call the Maxtors quiet because they have a noisy/normal power supply, and not a PSU specifically designed for low noise (as I do - noise is both very subjective and relative, so it's hard to make comparisons and get advice for extremely low-noise components).