It's a laptop drive. They're quieter (seek and idle) I can't hear my WD 2.5" at all, but the 3.5" are audible a few feet away.
You also have several options to go down.
1) Fit HD silencer to primary boot drive.
2) Replace boot drive with 2.5". Expensive per GB, and slow performance
3) Do 1 or 2 then then the extra 3.5" drives in a NAS.
I'm going to use the 2.5" HD in the HTPC as boot, then get D-link DNS-323 fit 320+250 into that, music and movies stored on the NAS. HTPC and gaming rig can then access both.
I don't think you can use NAS to play games off it though, LAN doesn't have enough bandwidth? But for music, docs, videos, drivers, software and other backup data it's a good idea.