I bought a UPS a year back to use in the server rack.
What I did not think of was the noise level. I think I saw the specs and saw a fan, but didn’t think it would be spinning all the time, or to be so loud.
Well, I was wrong and the fan was a bit louder than I could accept.
First thing I tried was the easy one. I just swapped out the fan with another one I had, a Noctua. Known for their silence.
That worked for 5 minutes, after which the UPS decided the fan had stopped and turned itself off. The fan WAS running, though.
Apparently there must be an incompatibility with the RPM-sensors – perhaps.
Another solution was needed..