My 60GB and 40GB are both usually "silent" (as in, I have to focus to hear them). When I start heavy gaming, you can hear the fans kick in, but it's by no means a "whoosh" of any kind. Generally it's at a volume where I don't even notice them kick in. I would once again have to focus (though not very hard) to hear them.
Simply put, mine are NEVER distracting...at all. My 360 sounded like a mini-vacuum. Ugh, that thing was annoying.
Like everyone said, give your PS3 plenty of breathing room.