I'd guess it should be either worn out (vibrating) or some obstacle.
When trying to replace the
microfilter myself I accidentally extracted the
blower (item #3) instead.
After I put it back it just stopped working. Feeling exhausted
with that limited access/visibility I called the dealer. They tried to impose computer diagnostics in a few days.
So I had to fix it myself by reinstalling again.
A handy, ready to kneel/lie down person with
these tools (from
here, "Cabin Filter | Mounting Instruction") should be able to check it.