toilet is making a slight noise
 

Our guest bath has an American Standard one piece toilet and recently has started making a hissing noise. I do not see any water movement in the tank or the bowl when at rest and there is no leak on the floor. It appears to have a Fluidmaster type ballcock and a standard flapper valve. Should I start by replacing the flapper ?

Check the float and see how far up the water is rising. The tube sticking straight up in the middle of the tank...if water is rising over that and flowing into that tube, it will cause hissing. The water should come up to about 1/2 inch from the top of the tube.

Randy

Put a bit of food coloring in the tank and check to see if any of it has shown up in the bowl in 30 minutes or so.

It could need a new flapper, or it could be solved by cleaning the flapper and the drain and wiping a small amount of vaseline on the mating surfaces.

Heh he, he said a small amount of vaseline on the mating surfaces.

The hissing is, most likely, water slowly entering the tank through the ballcock valve. If you simply lift the float with your hand and the hissing stops, that tells you the water flow is the cause of the noise. From there, use the suggestions above to locate the reason the tank level is slowly dropping to the point where the valve begins to refill--creating the hissing. Number one suspect is the flapper as they will deteriorate just by sitting in water over periods of time, especially if any toilet bowl cleaners are added to the tank.

Yep, probably the flapper. If the water is up to the overflow, it's the float valve, if it stays slightly below it's the flapper. Either way I'd change all of the guts. Well, actually if it was my house I'd swap an older AS for a Toto ;)

Turn off the supply valve and see if noise stops. If it doesn't, the house is haunted.

Snake!

My toilette makes a BIG noise when I sit on it....

When I lift up on the fluidmaster float the hissing does NOT stop so I don't believe it is the valve. The water level in the tank comes up to about 1/2 " to the top of the overflow tube so it's not that either.I'll start by replacing the flapper and go from there. Thanks

Mine starts to smell too.

Fluidmaster fill valve is not to difficult.
The shutoff valve might be stuck so be easy with that(soak w/wd40, work back and forth, and use backup wrench to isolate). Mark existing water line w/pencil. Take old off, and on new twist base flange to match the same height.
Clean. I used a light smear of silicone lube.
Reinstall with valves pointing in right direction. Pop off cap(1/8 twist) and cover with cup to flush out lines then put back on.

Replace the shutoff water line with same length while you're in there.
Follow directions etc.
New ones have a nifty anti-leak shutoff gizmo which is touchy when testing.

OK last week I replaced the flapper, while it looks great the toilet still is hissing. The ballcock is a Fluidmaster 400 so I bought a replacement seal, this is the seal that goes on top that supposedly stops water from leaking. Put it back together and flushed twice all is good. Fifteen minutes later my wife says it's hissing again ! Sure enough it is, the same as when I started. No leaks on the floor. Could the Fluidmaster be bad ? I was under the impression that this seal is the only working part of the design ? Should I just replace it ?

Does it make this sound "Brraaaaaaap" when you sit on it?

how old is the toilet?

how hard is your water?

This reminds me of Dave Barry's story about toilets and rental houses. :D

Have you checked the muffler bearings?

Slide the float a little further down on the rod to create more pressure on the valve seat.

Many won't do that. And I hope you meant make the rod longer. But, you bring up a point. Maybe some water has gotten in the float.

Well really my intent is to submerge more of the float at the top of it travel, to exert more pressure on the seat.
And yes, effectively 'making the rod longer.' A fluidmaster works slightly differently than the old rod and ball arrangement.