I've been meaning to take a video of this for a while, and I finally got around to it this morning. My apologies for the lousy quality; my phone is terrible, and my camera doesn't take video. Also, apologies for the dirty chrome

My Duetto is drawing from the built-in reservoir. When it's been turned on for a while without running, the first time the pump runs, I get a weird "grating" sound that quickly dies down. You can hear it in this video of the first warming flush of the day.



Is this normal? What's the cause?

Air in the hoses?

That was the first thing that came to mind. Is it normal that it keeps happening?

The sound is not very clear, but I think it sounds exactly like my Duetto. I guess it is completely normal.

I had the same sound with my Alex (HX) when I was running off of the reservoir. When I plumbed the machine in, I never heard it again. I think it is normal for running off the reservoir. Why it does it though, I don't know.

It is easy to see that water in the intake hose would like to flow down, due to gravity. The question is where the air comes from, because the end of the hose is submerged in water reservoir...

Plumbed-in is a different story as water intake is pressurized all the time.