Hissing Fluidmaster

About 2 weels ago I finally got around to replacing my old leaking fill valve with the Fluidmaster with the leak guard, i didn't install the leak guard though....anyway i had trouble with it from the start but about 4 days ago i thought i had the bugs worked out.....
today i noticed a hissing sound so i took the lid off and there has been a continous low hissing sound all day....
moving the float cup up doesn't stop it, adjusting the water level doesn't stop it.....it's driving me crazy...
it doesn't look like the water level inside the tank is changing......
any ideas? or do i chalk it up to a defective valve......

You need to remove the top of the Fluidmaster and check for debris at the seal....

valve

It has debris inside the cap, or the valve stem is cracked, or the valve mechanism is defective. ALL will cause the same sound.

haha i did check when i installed my brother's new fill valve.. luckly it works great...its wider than the old one..so there is less space...
and i precisely measured the waterlevel xD

I'd ditch the Leak Sentry and make it a regular fluidmaster 400 A...