If the noise comes from movement of airflow, the cause of noise is connected with foreign bodies laying in suction point or air outlet. The solution is to remove them.

But more frequent the cause of noise is connected with inappropriate selection of fan.
In this case we suggest to replace the fan with other one, which is more quiet (usualy with bigger diameter and lower speed) or use some silencing material.

If noise is of mechanical origin the cause is connected with physical contact between moving parts, wrong bearing or vibrations of metal sheets.

If noise is of electric origin the cause is connected with eccentric between rotor and stator or vibrations of winding.

In each of these cases we suggest using antivibration supports (pendulum-type vibration damper supports) and antivibration connections made of rubber, both in suction point and air outlet.