In my experience, sometimes it is found that AIR filter becomes dusty. After cleaning or changin AIR filter alarm also removed.

I think cleaning the air filter is very important.

How long do you clean it?

Cleaning depends on environment of NE where it is located. For example, when NE resides on core layer, cleaning is not required most often, because optimum environment maintained here. But in access layer nodes, most of the time they resides on remote locations in tough environment. In that case we clean every 3 months, sometime replace in 6-12 months time span.

Great share!