Small trickle into toilet bowl, flap and valve seem fine
A leaking valve can also cause this kind of leakage  rust, scale &amp; small gravel can also cause the valve to leak. Some valves can be easily disassembled with the water off. A cup or glass put over the top and the valve turned on to flush the debris out. Reassemble with the water off and see if this helps. The float adjustment would be a quicker check as @jack suggested+. a video on how to flush a kohler fill valve. this is really quick and just 1 of several ways to clear the debris out. Some also have 4 screws on the top those you need to take apart and flush with the cup. some have tabs that when pressed in release the cap. Not all valves can be cleaned and some like fluid master can be pulled off the stem and a new valve installed in seconds. I hope this additional information helps.