The only adjustment on the valve is the height (fill level) where it shuts off.
Toto uses a couple of different valves, if the one you have does NOT have a plastic screw on the top, then it is made for them by Korky. That one has one wear part in it. You might try replacing that cap for about $2.50 (available at Lowes and many hardware stores). While you've got it apart (it's easy, no tools required), you might clean the screen. Other than that, the things generally are pretty quiet.