Sounds like you have a Type B valve (made by Korky in Wisconsin). Service it in accordance with these instructions: Toto Fill Valve Servicing Instructions
Don't overthink it. Most of the time, just cleaning the parts or replacing the little cap with the rubber parts in it (which cost like $3 at Lowe's) solves the problem.
Here is a simpler video with servicing techniques from the manufacturer:
Sometimes, if you hear it pulsing on and off after the toilet has been sitting for a while, it's not a problem with the fill valve. The fill valve is acting correctly to try to refill the toilet because the water has slowly leaked. Check by marking the water level in the tank with a pencil, then turning off the water to the toilet and letting it sit for a couple of hours. If the water level drops, it's almost always because you need to change the flapper. The Korky GMax flapper is available at a lot of hardware stores (Korky "Fits Toto" GMax Flapper, which is the one made by Korky for your toilet and likely came with it) Korky GMax Flapper. Or the universal Korky 3" flapper is available at Lowe's.
Let us know how it goes.