Generlly, the room has to be pretty quiet to hear the bubble squeeks.
This is normal, you can clean the diffusers monthly etc real good in bleach, I add about a 50/50 water bleach mix and let soak for about 1 hour.
Then rinse good, soak in dechlor for about 15 min, return to the tank and add a little dechlor to the tank itself.


Regards,
Tom Barr