Another day another mystery toilet sound haha. I'm hearing a soft hissing noise so I checked the usual culprits:flapper, overflow and they seem fine. Didn't seem like water was moving anywhere in the toilet so I turned water off to the toilet and emptied it.... Still hearing that sound! Is it the pipes themselves? Could it be... Gas?? There's a gas line somewhere near there in the exterior wall next to the toilet but it's sounding the same as a loose flapper basically. Any thoughts?