Quickmill Anita makes high pitch sound during the pull

[SL]

I own Anita for less than 2 months. It started about 2-3 weeks ago. When I was backflushing with the blind disk I heard the high pitch sound for a few seconds. But recently I hear it more and more often even when pulling espresso shots.
I backflush with the blind disk and clear water every couple days. Once (after the month I owned Anita) I did it with Cafiza following the instructions. I do not remember whether the sound started before or after cleaning with Cafiza.
Anyone knows what could be a problem?

[TimEggers]

The most common culprit is water resonance of the OPV spring. This isn't an issue (isn't a sign of machine damage) and is most often regarded as an annoyance. If it bothers you you can try to turn the OPV adjusting nut back and forth a few times. Sometimes this can make it go away.

Further reading: strange-noise-coming-from-my-andreja-premium-5-months-old-t4915.html

[SL]

Thank you, Tim. I should've searched the forum before posting my question. It's good to know that everything is fine with the machine.

[poison]

Lol, my Expobar does the same.