AirGradient One v.9 making high pitched sound

[SteveA]

I have two AirGradient One v.9 units, one in the living room and one in the bedroom. The one in the bedroom has started making a very quiet high pitched sound. It’s not noticeable during the day, but at night, it’s quite audiable, and I’ve started turning the monitor off at night.

I plan to do some testing to see if I can narrow down what’s causing the sound, like swapping the units between bedroom and living room to see if it’s related to the power supply.

Any other ideas?

[Achim_AirGradient]

It’s definitely not a common problem so I don’t know what causes it but you might also want to check the PM sensor if something is partially blocking its fan. Pushing in compressed air might help.