After flushing, the toilet goes silent for about 15 seconds and then the tank starts refilling. What may be causing this? Thanks.

I would guess the valve that the float arm pushes in is hanging, then slowly releasing.
You could remove tank top(not yours mam/sir?), flush toilet, then lift arm and look at where float arm contacts valve immediately after lifting arm, could do with water turned off, so you can lift from full down position.
A lubricant may fix.

Please lift the tank lid look inside and tell us which type is you fill valve, see the images, Thanks.

John

Please lift the tank lid look inside and tell us which type is you fill valve, see the images, Thanks.

John

Mine is the one on the left. Thanks (in advance).

Your float can's hanging up on the valve body. Shut the water off under the tank and flush and drain the tank. Wipe down the valve body and take and lube the valve body with some Plumbers Grease or Vaseline. Turn the water back on and give it a flush. Better now? Good luck and thanks for rating my reply, Tom

Hi lewbie,

Tom is correct fallow his instructions if that would not help then it is time to change the fill valve (fluidmaster) is not expensive will cost you $10.0, good luck.

John