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?
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.
@Achim_AirGradient I do have the same issue.
After a few months of use, the PM2.5 sensor fan was becoming louder. Much so, that I moved the unit further from the bed and finally unplugged it. Today I had some time to research this issue and disassembled the AirGradiant One, unscrewed the PM2.5 Sensor and (following a YT video) pried open the sensor to get the fan out.
First thing: super impressive that it was so easy to disassemble 
You basically only need TR6 torx and a metal prying tool (I used my ifixit kit).
The fan itself was covered in dust, but nothing was blocking it and it was way less dust built up than I usually see in my laptops. I lubricated the fan using silicon oil and just by blowing you can hear the difference it made. I will assemble everything now and hope that it will stay silent for a while now.
Maybe these sensors have some quality issue regarding lubrication?
Anyway, I hope this can help others to debug and fix their noise issue.
Cheers,
Lukas
I can’t edit my previous answer just yet. However, I wanted to add that the fan noise came back after a few hours. So lubrication did not work. I’ll try using WD40 next time and if this also does not work, I’ll find a replacement fan.
Hey @Lukas
Please do contact us via the support form here: The First Professional-Grade, Affordable Air Quality Monitor and, if possible, provide a recording of the noise so we have better context. We are happy to send a replacement sensor as well!
Sorry, I haven’t had time to work on this until now.
I’ll send you the video @Altair_AirGradient.
I ordered a few other fans to replace the one I thought was the issue. However, upon testing and recording it while disassembled, I noticed that the fan itself is not actually the issue (the Plantower fan is quieter than the replacements I got). The source of the noise is the fan vibrating against the casing. This can easily be fixed by adding a thin layer of something to avoid the fan case hitting the sensor case.
The old fan does have some kind of double-sided tape on it, but it’s not very sticky anymore, which might explain why this only appeared after a few months.
This is definitely a production issue with these sensors. They should add something better than just a small piece of tape.
