APC SURT3000XLI noise problem

[Anonymous user]

Hello, I have an APC SURT3000XLI UPS 2 years about and recently I noticed a weird noise which takes place even if I have the UPS turned off but pluged into the utility power. It sounds in Online or Bypass mode too. It only stops if I un-plug the UPS from the utility power. When I plug it in again it starts after the battary if fully charged. Is this normal? I recorded an mp3 file. First it's the UPS pluged to utility power, after the "click" sound I switch it to bypass (still there is that noise), then switch it back to Online and unplug it. In the end (Online mode no utility power) I listen only to the coil sound. Thanks in advance!

[Anonymous user]

Thank you for your fast response! I clean the fan and the grill often, so no it's not dirty. If it was fan's noise why it stops when I unplug the unit from the utility power? I don't know if it started recently or it was from the first day of use because I have the UPS in a machine room. Should I try to stop the fan when the unit is plugged in utility power to check if the noise stops?

[Anonymous user]

I tried to stop the fan with a pencil when the UPS was off and the noise still exists 😕 I assume that it's coming from the back side of the UPS near the input section. It only stops if I unplug the unit from the utility power. So my question is: Is that sound normal for this UPS or shouldn't exist at all? When I unplug it I only listen to the sound that coils make and the fan noise.

[Anonymous user]

Unfortunately it's out of warranty. I have the UPS installed in a machine room so I am not bothered by the noise. Since it's not going to harm any of my equipment which is pluged on it or the unit itself it's ok.

Thank you very much for your help!

[Anonymous user]

Hello Common Sense. No, I don't think so. I also tried the UPS in another 2 buildings, also the one was 80km away from here and the noise still exists... An update tha may be useful is that I checked the UPS output with an osciloscope and there is some distortion near the zero point. The top +1 and the bottom -1 of the sine wave are perfect and way better than my mains power but not the rest of it :'

[Anonymous user · Accepted solution]

Sounds like you may have a harmonic issue on your input power, do you have any large rectifiers nearby?