After using the Avalon Mini 3 for a really long time, I gotta say that only thing that really annoyed me was the rattle noise caused by loosely attached fan exhaust grille. I've seen also many other people reporting it, so I suppose it is a type error. During my long term use it just kept escalating and I finally just could not stand the fuckin' rattle noise.
So my solution was a quick fix by focusing on the position where my grille was flapping the most and adding white glue (PVA glue) there.
It is eco friendly and non-toxic glue type, so I should be fine in regard of my house air quality. Of course the exhaust air is quite warm and white glue tends to melt in hot temp, but so far my fix has stayed in place perfectly.
(you can click it for bigger photo, see upper left area of visible grille in photo)