It is a specific issue. It does not affect all units and would not be noticeable with even a moderate noise background. It is approx 2200hz and will drive you out of your mind in a silent environment. It can be there from day one or show up even months later. I had 2 and one had it out of the box the other showed up at around 10 days. That being said I have owned used Mac minis since PowerPC days and low cpu load the studio is louder than ANY Mac mini. Last I researched it Apple does not know how to fix it. They pull out the parts cannon.I have two Studio ultras absolutely no noise from either of them. Even at high workloads ...... silent. Your "Known issue" is rubbish in my experience. Does your Studio make a noise?