I have had three I-9PSL in my house for about a year now. I noticed last night the one in my room suddenly had audible fan noise. This high pitch hum is audible from about 8 feet away.
Checking my other units of they seems to have no audible noise, at this distance. I attempted to blow out the unit with compressed air to no effect.
I found this old post describing a fix someone found for this issue. I am going to attempt this fix today.
Just wanted to make folks aware this is still a potential issue that occurs with these units. Will update with my results later.