When I flush my toilet, it makes a whistling sound? How do I correct this?

Most likely a washer on your fill valve. Remove the tank lid and cup the top of the fill valve in your hand, squeeze a bit and flush. Did you feel vibration?

I have a fil-master (black plastic) what do I squeeze?

Cup your hand over this Fillmaster valve repair

Sorry Bob if understand correctly he has a Fluidmaster fill valve, Ferchak please see the images below

Looks like the OP said Fillmaster so that's what I posted a picture of. Similar products but fillmaster has an adjustment screw on top of the valve washer

Sorry Bob, I miss read Thanks.

John