I have a Gerber toilet with a 99-646 Pilot Valve and just recently when I flush the toilet a vibrating noise
Is made as the water if filling into the tank after the flush. Could this be a sign that I need to replace
The Pilot Valve? If so how do I go about doing that?

It could be your fill valve, but more likely there is a loose washer in your toilet stop (shut off vavle under the toilet). To check this, shut the water off to the house, drain pressure off by opening a lower fixture, if there is one, then remove the pacing nut that holds the stem in the stop. Screw the stem out, and see if the washer is loose. Some you can tighten, others, its best just to replace the shutoff. As for the fill valve, just shut the stop off, diconnect the supply line from the bottom of the tank, then remove the nut that holds the fill valve in place, and remove the fill valve (make sure to sponge or shop vac all the water out of the tank before doing this.) Then just install the new one the way the old one came out.