Ok so it’s not really a ghost flushing your toilet. Well, maybe in some cases it is but more than likely it’s the flapper. Here’s a good illustration of how to fix that.
How To Fix A Noisy Toilet
This is a pretty common problem. Phantom water noises in the toilet usually heard in the middle of the night (because it’s quiet). Most of the time this is caused by a worn out flapper which is real easy to replace but sometimes it is the rim on the flush valve. In the case of the rim on the flush valve being worn, you would need to replace the whole flush valve as he has done in the video. But I would start by just replacing the flapper. In my experience that does the trick most of the time. Either way it’s a pretty easy fix.
Kevin Hicks 