I spent years replacing toilet flappers when the real problem was the fill tube
For like 5 years I'd get that ghost flushing sound and immediately run to the hardware store for a new flapper. Must have gone through 8 or 9 of them across two different toilets. Then my neighbor who used to do plumbing came over to borrow my impact driver, heard the toilet running, and asked when I last checked the fill tube height. I told him I didn't even know that was a thing. He pulled off the lid, bent the little plastic clip holding the fill tube so it aimed straight down into the overflow pipe instead of sideways, and the noise stopped right there. Zero parts, zero dollars, took him 10 seconds. Now every time I hear that sound I check the tube position first, and I've fixed three friends' toilets the same way. Anybody else have a fix that was way simpler than what they were doing for years?