Apc Es550 low humming/buzzing sound.

[Vanya Hargreeves]

I had this usp, since 2018 and a few months, back replaced the battery. Now it seem to be emitting like a very low yet audible humming. Like a bug zapper.

It on Ac power and when I got the new battery I charged it 18 hours. It only just now it doing this. I almost inaudible but won't to know of this is normal?

 

[Rroff]

Only time mine hum/buzz is on switching over to battery power or sometimes when charging the battery below 50%.

If it has suddenly started humming either there is a loose connection, damping glue stuff used on inductors, etc. has dried out and/or transformers have shifted a bit over time or some of the capacitors are no longer doing their job properly which may or may not be something to worry about.

A common problem with APC UPS, especially the oversized extension lead style ones, is that over time the capacitors experience a lot of heat and a lot of heat cycles and start to perform less than they should.

 

[Vanya Hargreeves]

If it helps it a very low humming like close to whisper humming.