All my external HDDs have fans which include an ANTEC MX-1. Most of my HDDs are 7200 - 10000 rpm. The drives get really hot which is an enemy of HDDs. You cannot hear the fans in any of the enclosures. Better safe than sorry is my mantra.
I agree about using enclosures with fans. I'm just saying that the MX-1's are not readily available anymore, we need to find a new actively cooled alternative enclosure. About the noise, I can hear every one I've ever owned, consider yourself lucky that you got nearly silent models, or you just cant pick it up. I've had 5 Antec MX-1's and none have ever been silent, but they are quiet enough for the peace of mind I get running the drives at lower temps for longevity. I've never lost a drive in an MX-1, but I've 2 in TT BlacX enclosures. Probably partly coincidence, and I'm sure partly heat. I do not use anything but AVGP drives because there is no advantage to using 7200-10000 rpm drives in these dvrs. I tested faster drives for months and there was absolutely no speed advantage, so I stayed away from the heat of the faster drives. I use nothing but the faster drives in my pc's, for obvious reasons.