The S9 should be quiet as a mouse. When mine made any noise, it was because the humidifier lid wasn't fully closed and latched. Were it me, I'd run the mask fit routine (mask on) and feel around the machine, especially the humidifier to unit junction and humidifier lid, hose, etc, for air leakage. You may have a seal in the unit leaking (or missing).
Check the gasket in the top of the humidifier. It's removable for cleaning; and has to be reseated just right.
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Disconnect the humidifier from the blower. Attach the hose directly to the side of the blower. Turn the machine on. Do you still hear the noise? If so, the machine is defective (or maybe the hose has a large leak). If not, you have isolated the noise to the humidifier. This is not uncommon. Carefully check and re-seat the seals. If you press down on the humidifier lid, does the noise reduce?
This noise most likely is from a loose fit on the humidifier container, or even a mis-aligned silicone gasket in the humidifier tray. Take the humidifier container out of the humidifier and inspect all the seals. Try re-inserting it firmly, and turn on the unit keeping the outlet tube blocked. A leak in the unit will be noisy. If the noise continues, remove the H5i humidifier from the blower unit and hook up the hose directly to the blower outlet. If the noise continues, the blower unit has a problem. If the noise goes away, then again, it is the seal where the blower outlet goes into the humidifier.
Your unit is under warranty, but this sounds like a problem that can be solved with some simple troubleshooting and reassembly.
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AS others have said, make sure the gasket in the humidifier lid is in correctly and it is closed snuggly. If it isn't closed tight, it will be loud.
I have had this happen to me and it is because I didn't press down firmly enough to close the lid.
Good luck to your husband with his CPAP therapy and to you with getting good sleep.
Hang in there for more responses to your post.
Make sure the lid is fully closed and latched. It will still run when the lid is loose and when that is the case it makes a much louder sound. Also, make sure the hose is properly attached. May sound like a dumb answer, but my respironics is very quiet EXCEPT when I have added water and the lid did not latch and seal properly. While this may sound too obvious, it is the only thing I could think of that would make this loud noise.
Sounds like something is wrong...
I'm pretty sure all resmed s9 machines have a little bit of air coming out the front.
If you unplug the machine and take off the humidifier and the filter cover and filter, you can plug the intake hole with one finger and blow into the out take hole and hear the air coming out of the front of the machine like a very slow leak. If you hear air escaping any where else, such as on top or on the sides, then something is wrong.
If it's the motor, well, I don't know what a defective motor sounds like. Does the sound change on exhalation or inhalation?