[V12|V12]

Ball bearing fans can quite often develop some extremely annoying and industrial sounding noises when you adjust their power with PWM.

Hrmm, I've tried that before and don't know how or what PWM has to PHYSICALLY do with bearings making noise. Unless the bearing is physically damaged or severaly worn, it will NOT make any noticeable noise based on the type of electrical control of voltage powering the fan. PWN, Or any other type of speed control doesn't have an affect on physical bearings, unless you're touching the rotor... I think it has more to do with sine-wave noise and frequency... the bearings and rotor are totally separated from any current produced by the magnetic field/coils...

People have had some success taking fine grain sandpaper and sanding the blades of the rotrons smooth. I have heard that this will reduce noise considerably...

Again... I've had every fan I've gotten form a surplus store tested before I bought it and NONE of them make these mysterious noises. That and when I'm hand picking a fan, I spin and listen, shake and move the fan to vaguely test for wear/damage etc... Unless you get a full speed 172mm+ fan (4500rpm+) THen if you're running them (12v fans, anything more just won't like lower voltages than 12) at full 12v, and even then they don't make THAT much noise as compared to a full 12v 120mm... in my exp. Again, I just think people are making poor choices when they choose them? I've got LOTS of experience with big fans, I basically spend hours and hours trying them out, to get the best one and even the one's I don't choose are in great running order. :shrug:

People sometimes also have to oil the bearings of the Rotrons which came from surplus stores

I would NOT recommend that at all! Unless you totally overhaul the bearing (IE soaking them in solvent to remove all grease and buildup), b/c of all the fans I've overhauled, every one is grease packed, usually some sort of molybdenum disulfide grease, b/c it's great for high temps, rust inhibitor, resists dust build-up and lasts MUCH longer than oil. Mixing oils with grease packed bearings can result in serious degradation of the grease and result in strange compounds which could actually attack the bearing, depending on the type of oil added and grease inside etc... blah blah.

Either way... if you've got the space for a nice MONSTEROUS fan, I'd recommend trying it out, you won't be sorry. Though, most of those types of fans are around 18-20W+! So if you can find a really high wattage Rheostat (very pricey!) or a fanbus that can handle 18W+ then I'd get one... PWM would need some tweaking based on, I guess others no so good noise experiences? Right now I'm planning on getting more Rotron 120x38mm Whisper XL's since they are ultra quiet, reliable and draw tons of air with minimal noise and high static pressure capabilities... Good luck all!