A rifle bearing is Coolermaster's enhancement of a sleeve bearing with increased lifetime.
So, noise: ball > sleeve > rifle
but, lifetime: ball > rifle > sleeve
AFAIK, Panaflo's hydrawave fliud bearing is based upon a sleeve fan.
Down at Silent PC, in a review I read the rifle bearings were pretty good - "better than Vantec Stealths".
In the forums, ppl did not agree. Stealths are well regarded here.
I'm confused - I need to buy 3 case fans as replacements with use of a sunbeam fanbus. Maybe I'll just order one of each fan...