PC Apex Review posted a new review up on a fan offered by MNPCTech.com

The general consensus is that there are only two types of 12V DC fans, sleeve bearing and ball bearing and the latter is the superior design. Neither assumption is entirely true. The second widely held belief is that ball bearing fans are the quietest fans you can buy. I actually had someone tell me recently that he had installed six fans in his computer case and since they were all "ball bearing" fans you could barely hear them. I just smiled and thought to myself, 'The quiet you're experiencing is no doubt due to hearing loss caused by excessive fan noise.

NMB-MAT Panaflo L1A Fan w-RPM Sensing