Not sure if EliteRetard is trying to be funny or what he is talking about. At idle, Raptors are as quiet as a 7200RPM drive and are inaudible over typical ambient noise (PSU/CPU fans, etc).
The vibration anecdote is just stupid. I have never seen a drive, and I have owned multiple 15k rpm and old school SCSI 10k drives, that would move themselves when placed on a hard surface, let alone move a case it was installed in. A desktop hard drive will not function at all if it was vibrated hard enough to move a case.
Cat noises were a joke, yes.
Just did a quick youtube and this was on the front page:
http://www.youtube.com/watch?v=n1KdOpV7r_k
You might not have ever seen a HDD vibrate, but I know for certain that they do.
And what I'm talking about isn't a violent thrashing like a washing machine gone mad...just a constant vibration/rattle (perhaps like a phone vibration?) that was enough to cause the case feet to loose friction and drift kinda like a puck on an air hockey table. It didn't move very fast, but it was visible...
I know of a few other examples of computers/laptops vibrating like this, but only once was the combination of things right to where I saw it move like that. That's what made it so funny.
Edit: Here's another video of HDD vibration
http://www.youtube.com/watch?v=_LRkn9ItsNk
And these are just 7200RPM (Seagate) drives, he had 2 3.5" WD 10K drives hard mounted in a custom case....and they definitely caused vibration.