Jadnashua
Retired Defense Industry Engineer xxx
Some styles of toilet filler valves can cause chattering. This is often a random thing accompanied by a slow leak with the flapper valve so the tank refills at odd times. Try turning the supply off to the toilets, verify that the tanks remain full, and see if that correlates to anything. You might want to check the water pressure as well. If you have high pressure, again, some toilet filer valves can't handle it and will make some noise. Fixing a leaking valve may mean that there's now no outlet for that pressure (spike?), and you now have more static pressure than you had before.