I just moved into a house and am having trouble flushing the toilet. Sometimes the toilet would make hissing sounds randomly at night. Could this be a leak?
Clearly your toilet is haunted by ghosts of turds passed.
the fill valve could be leaking and making that kind of noise.
you can replace the inside mechanism for not too much cost.
It could be that the mechanism inside the toilet is wearing out (as johnpost suggested). It could also be a clogged vent stack. Or it could be both. Those would be the first two things I would look at though.
A leaky fill valve would constantly be allowing water into the flush tank, rather than “sometimes” and “randomly” be making the sound.
What’s happening is that the flapper valve is slowly allowing water to pass out of the tank and into the bowl. This gradually lowers the level of water in the tank, consequently, the float drops, causing the valve that it controls to refill the tank. As the water in the tank rises to its optimum level, it raises the float, and eventually closes the fill valve.
First suggested fix: thoroughly clean the flapper valve and its seat (don’t scour them, as that might actually cause, or worsen, a leak; just give them both a good wipe-down.
Second suggested fix: replace the flapper itself.
Third suggested fix: replace the valve seat.
You can try to check your toilet for homes or cracks including its flappers, tank balls, seat disks and flush valve seat. Remember to use gloves and touch to see if there’s residue. If there is residue on any of these parts then you might need to replace it. Go through this checklist and make sure there isn’t a leak in any other places in your toilet.
There’s a famous song about ghost turds: (SFW)
That sounds right to me, too. When we had that problem, we followed the “route” along visually and saw that the chain had become crimped. So it was occasionally not letting the flapper valve close all the way.