Toilet noise after water shut off

[Bcunning]

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?

 

[Reach4]

Gas meters often make a hissing sound while you are using a bunch of gas. But I would not think you would be using a bunch of heating gas in Dallas October. Maybe cooking gas?

Loose flapper might make a dripping sound, and then the hissing comes from the toilet refilling intermittently to refill the lost water. With the stop valve closed, no refill is happening.