Good question. No, it wasn't a rattling noise. It was a rubbing noise. I hear a variation of rubbing with many fans, especially if they use sleeve, rifle or a really cheap HDB/FDB. DBBs have a different noise that is, to my ears, more electronic as the balls rub together, so it's really the sound of metal on metal.
It's pwm "ticking" noise - very bad side of 184 model because of the poor electronic quality of new Silverstone oem partner, 183 (182 & 181also) is ok, they were made by another partner
