Quiet external harddrive: noiseless backup solution

Seems topic wasn't touched in about a year, so I decided to ask the question again.

What quiet external hard drive can you recommend?

I'm trying to decide what should I pick as my external backup, but noise level is deciding factor for me.

I have two options on the table at the moment:
1. External harddrive to be plugged into AirPort Extreme
2. External harddrive to be plugged directly into MBP.

If I'd go with AirPort option, then the drive needs really to be silent - and no vibrations - as it would be most of the time on. Or can AirPort spin down hard drive when it's unused? How TimeMachine does it's backups: constantly or once in a while?

If I'd go with direct connect to MBP option, then I can probably live with noise for a limited time the drive is connected to MBP. I'm no stranger to *nix style scripted backups too. But that's not really option I want to live with.

What is your experience setting up noise-less backup?

P.S. Googling made me sad. Most people only look (or better say listen) to hard drive produced noises: seeks or motor noises. But disregard the major noise maker: vibrations. In my PC rig most of the noise during idle times produced mostly by vibrations of the Seagate hard drive. That was not the last reasons why I went ssd in my UMBP.