Every time I flush the toilet as soon as I start flushing I hear this sound like air is slowly seeping out of a balloon, but the noise seems like its by my water heater

Yes I did see your past post , Thanks. Ok here is the best way I can explain it: The way my house is set up is that I must walk down a short hallway before I walk through the doorway of my bathroom... in that hall way is my furnace & water heater... the water heater sits right next to the doorway opening of my bathroom.
This is why it is hard for me to determine if the hissing sound is coming from my toilet or the closet where my water heater and furnace are. To me it sounds like it is coming more so from the water heater. I replaced my water heater 1 yr ago. No water or wetness is any where around the water heater. The pipes are dry also. Now this "hissing" noise seems to start at the moment I start to flush, once the toilet tank is filled up again the hissing sound stops. That big round thing in side my toilet tank does rise once it is refilling... but I noticed that the tank itself doesn't empty all the way... there is about 1 to 2 inches of water left at the bottom of the tank before it starts refilling itself. I hope you understand my problem better now, Thank You,
Stephanie

Please do not open a new post each time you reply. We can not see any previous discussions. Post reply in the box below. I would think, from what you say, there is a slight clog or restiction in your fill valve. They can be rebuilt but replacing them cost about $10.

this "hissing" noise seems to start at the moment I start to flush, once the toilet tank is filled up again the hissing sound stops. BINGO! You've just isolated the poroblem.

there is about 1 to 2 inches of water left at the bottom of the tank before it starts refilling itself. This is normal. Don't sweat it!
For the hissing shut the water off to the toilet at the stop and remove the lid.
Now unscrew the three screws on top of the ballcock and pull the float ball and stem up and away. Place a pan over the open ballcock and turn the water back on to flush out the supply. Check the washer and push it in tight. Reassemble and test. Better now? Good luck, Tom

Ok here is the best way I can explain it: The way my house is set up is that I must walk down a short hallway before I walk through the doorway of my bathroom... in that hall way is my furnace & water heater... the water heater sits right next to the doorway opening of my bathroom.
This is why it is hard for me to determine if the hissing sound is coming from my toilet or the closet where my water heater and furnace are. To me it sounds like it is coming more so from the water heater. I replaced my water heater 1 yr ago. No water or wetness is any where around the water heater. The pipes are dry also. Now this "hissing" noise seems to start at the moment I start to flush, once the toilet tank is filled up again the hissing sound stops. That big round thing in side my toilet tank does rise once it is refilling... but I noticed that the tank itself doesn't empty all the way... there is about 1 to 2 inches of water left at the bottom of the tank before it starts refilling itself. I hope you understand my problem better now, Thank You,
Stephanie

Stop buy Home Depot, Lowe's or a hardware store and purchase a Fluid Master seal.

Turn off water to toilet by closing valve underneath the toilet tank. Flush toilet.
Remove tank lid. Reach down under float, lift float and grasp the shank. While lifting the float and holding the shank turn the cap on top, 1/4 turn counter clockwise and remove it.

Either place a cup or small bowl over the shank or hold your hand over it and turn water on briefly, about 5 seconds. This will flush out any debris that might be in the pipe.
Replace the seal in the cap and put the cap back in place making sure it is properly connected.

Turn water back on.