My toilet is whistling. It does not whistle during a flush, or while filling it up.
It does whistle when I shower, when the washing machine is used, when the neighbor downstairs uses water, and randomly at night. I changed the flapper but it still whistles.
Whistling began after city came and changed the main water meter (I live in an apartment).
Building is 50+ yrs old. Toilet was likely replaced in 90s.
Any ideas? Thank you...