S9 AutoSet - Noise at the breathing out!

[PaulaO2]

LOL You really want me to get one of those, don't you?

[Sleepster]

I'm just sayin'. These older Series 50 machines are on sale for a limited time. Once they're gone, they're gone for good.

But seriously, I have a Series 50 machine and it's an awesome piece of equipment. Very reliable and will run directly off a 12-volt battery.

[gspell68]

I get that noise, too.
I just assumed it was the hose. A hose will make that whistling noise with air passing through it just from twirling it around.
I never really thought to investigate it.

[Paptillian]

Honestly didn't read through the thread, but I do notice a sound from my S9 on exhale. I never looked into it though I assumed it was coming from the H5i. It sounds a little bit like air moving over the reservoir chamber. Anyway sound or not, it's quiet enough for me to sleep!

[DreamDiver]

There's really not much you can do about the whistle.
I did a comparison of the M-Series Pro sound level to the S9 when it first came out and noticed it then.
I keep mine about a foot below the top of the mattress on the lower shelf of the nightstand.
That seems to mitigate the whistle volume fairly well.