Popping sound when starting machine

[yankees123]

I have a resmed s9 autoset.  I do not use ramp, but I do use a climate hose.
Is it normal as I start my machine and it begins to increase pressure at about 4-5cm. h2O it seems to pop air for a second then stops and continues to my set pressure?  Also if I inhale deeply it also "pops" air for a second.  Just want to make sure this is normal as the machine is new. I looked for some other posts and mostly this sound is related to rainout.  I have never had rainout and like I said it happens in the beginning when the machine first is turned on.  

Thanks

[DavePaulson]

Do you feel any moisture when this occurs?

[yankees123]

No.  Dry mask and dry tubing.

[DavePaulson]

Do you think it could it be your hose expanding from the pressure?

[yankees123]

Just wondering,the sound is coming when the air is reaching the mask.  Is this something other people experience?

[DeepBreathing]

Just wondering,the sound is coming when the air is reaching the mask.  Is this something other people experience?

Hmmm... maybe the anti-asphyxia valve in the mask is making the noise. Do you have another mask you can try to see if the same thing happens?

[yankees123]

Another mask makes same sound.  Sounds like when air hits mask it makes like a thump sound for a second.

[Walla Walla]

I think DeepBreathing is right. Anti-Asphyxia Valve.

[Crimson Nape]

if the pressure is too low on a FFM and you exhale, it will force the anti-asphyxia valve to close to avoid permeating the hose with CO₂.  This rebreathing feature is typical of all full face masks.  Nasal and Pillows masks typically don't have this feature since your mouth is exposed to the atmosphere.

[TASmart]

Could be the mask seals inflating. I can feel/hear mine as they inflate.