Hi,

Yesterday I had my main water line replaced (apparently it was leaking for about a week until a geyser appeared in my front yard). Today I found my sub-basement toilet was "hissing". I took off the top and the water level was up to the overflow, so I adjusted it to go back to normal. However, even with it adjusted, the water level constantly rises to the top of the overflow (even over the float). The hose going into the overflow has water constantly coming out of it (is that normal?). The water level rises so slowly that it doesn't ever rise past the overflow.

I have a Kohler Fluidmaster toilet with all original parts. It's less than 10-years-old. I'm not sure if it's a water pressure problem, but it is attached to my office and the sound is driving me nuts.

I'd hate to replace everything just to have it not be the problem. I'm on an extremely fixed budget since having the main water line replaced.

Edit:
There is no water leaking out from anywhere and my flapper seems normal (no wavy edges, not leaking with a color test). The sound is coming from the overflow, which I'm thinking is the hose attached to the pump-thing (whatever the ballcock is attached it).

When I turn the water going to the toilet off, the hissing stops.

Most likely some debris from the main line repairs got into water line and is now preventing the seal in the fill valve from properly shutting off.
Turn water to the toilet off at the valve underneath the tank
Reach down underneath the float, lift the float and grasp the shank.
While holding the shank turn the black cap on top, 1/4 turn counter clockwise. Remove the cap. While holding you hand over the top of the shank, turn the water on briefly and flush out the shank. Replace the cap.

The Widget Maker nailed it, Some dirt got in your line and now needs to be flushed out,
Good luck, Tom

You two are awesome. Thanks for the assistance (and picture!).