My Quickmill Anita has suddenly started making a very loud high-pitched squealing noise when pulling shots. The noise is intermittent; it comes and goes during the 22seconds of the shot.

I have removed the mushroom and it doesn't have any noticeable large accumulation of scale. The machine is used for home use only, was descaled about a year ago and is used only to pull about 10-12 shots per week.

Is it possible to say definitively what the source of this noise probably is?

Hello Patrick the most common squealing which may be what you're hearing is often a chirp from the Over Pressure Valve (OPV). Please read "Strange noise coming from my Andreja Premium, 5 months old" and see if describes what you're hearing.

My guess was going to be a noisy OPV as well. They will squeal like a pig sometimes.

My Anita will squeal at times when I backflush or even during the occasional shot.

When the machine came last fall I had to lower the pressure from well over 10 bar to 9. It slowly moved back up to slightly over 10 and I just had to lower it again. I did not notice any correlation between brew pressure and squealing.

I was told the noise was not a problem or fault and as long as my coffee is delicious which it has I'm not going to worry.

It's a simple fix. First take the valve apart, clean it, replace the seat, and adjust to the proper setting. The noise is like taking an inflated balloon and pulling the sides of the opening and letting the air out. In essence that is exactly what is happening, high-pressure water is slipping by the seat and make the noise. Some times you can fix it as simply as rotating the adjustment a couple of turns then adjust back to where it was and magically it stops.

If you have any questions, give my service department a call. You can reach them Monday thru Friday 7:30 AM to 5:00 PM EST at 518-452-5995.

Thanks everyone for the feedback about the OPV. I just took it apart and it indeed looks like the culprit (I'll be sure within a few days). The rubber piston-head that makes contact with the valve seat has a deep -and clearly off-center - ridge worn in it and it's clear that the rubber is no longer "live" due to the age and heat. So it is undoubtedly failing under high pressure to do it's job and like Chris says, it's logical that the noise would be coming from high-frequency vibration of this piston as the 9-bar water leaks by irregularly.

I put it back together again so I can continue to use the machine but I do intend to replace the piston. I certainly hope it's available as a separate part; it would seem a total waste to have to replace the entire valve just for a simple rubber disk.

Hello Patrick Chris Coffee sells the seat for the expansion valve ($4.95) available on their site.