Why do you use the pin number in 'Tone () and noTone () instead of the label' PIEZO 'you defined?
It doesn't affect your problem now, but it makes the code harder to read.
Try at the end of the loop, at the sequence:
the line:
digitalWrite(PIEZO, LOW);to add. Is it quiet then?
Helped me with an American police siren that wouldn't turn off.
I don't know why 'noTone ()' didn't work for me either.