I have a vintage 1990 American Standard Plebe toilet with a not-quite-as-old Fluidmaster float valve. Once in awhile -- not every day -- I hear the Fluidmaster run for a few seconds.
Is my problem likely with the flapper or its seat? Or is there some other possible cause? I don't hear or see any water running into the bowl, but maybe that's because it's too slow to notice.
Thanks for any hints on what the problem is and how to fix it.