I just replaced my fill valve with the fluidmaster 400 and when I turned the water on the noises began. Now whenever I flush I get the noises. Should I replace the flapper too?

Try closing the stop valve under the tank a few turns to see if it changes the noise. Sounds like a loose washer in stop valve. If noise changes, or goes away change stop valve. Or just change out stop valve only about $6.

Did you flush the fluidmaster like it says? In the molding process, some small pieces of plastic can get trapped in the ***'y. That's why you flush them out. Try that first, the directiuons are in the kit.

Yes, I did do that.

I'll try that, thank you.