My UMFF whistles at the little exhaust port holes up by the nose bridge if I have the pressure set for more than 14. (14 is my original pressure...doc had me try 16 and it really whistled) I think it may just be the physics of the thing...some kind of "venturi" effect.
If you use a lower pressure than 14, you may not have the whistle???
Jayne
ULTRA MIRAGE - Whistles
Whistling UMFF
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