Sharp FU-28H-S Service Manual page 23

This symptom
The purifier is making clicking
noise.
Sometimes a clicking sound is
audible coming from
purifier; sometimes, it is not.
Does not indicate a problem with the air purifier.
This sound is produced when plasmacluster ions are being
generated.
While this sound may grow louder or softer and may even
the become almost inaudible depending on the humidity of the
room where the air purifier is being used, the plasmacluster
ion effectiveness remains the same.
23
FU-28H-S