iMac late 2015 fan noise

Over the last few days my late 2015 iMac started consistently making a noise. Rather annoying ... persistent, but somewhat intermittent, a bit like digital version of grinding, like an old school hard-drive being worked really hard.

I found a number of posts on this topic, mostly recommending fan replacement, or resetting SMC, dumping all your mac configs and sharing them with the world, etc. However, a piece of information that stuck from reading dozens of posts and watching some youtube videos was that fan bearings seem to go bad after a while is some of the iMac.

Long story short: before investing $$$ in a new fan, try downloading one of the apps that allows you to control the CPU fan speed, and increase baseline RPM's a bit. For me, baseline 1750 RPM works like a charm. The noise pretty much completely goes away.

It appears that, over time, some of the fans hit a resonance at lower RPM's, which results in a very annoying sound. Running the fan a bit faster will do no harm to your CPU.

This may not solve your iMac Fan Noise problem, but is sure worth a shot.

Note of caution: this is a very different issue then when your fan is blasting full speed. Fan blasting at full speed may be providing needed cooling to your CPU. You should look elsewhere for a solution.