... When you resume towing, by putting your foot on the gas
pedal, you extend the tongue within itself, causing a clunking noise.
What I do is try to stop a bit short of an intersection, and then while
you are waiting for the light to change, ease forward a bit to take up
the "slack", releasing the brakes and extending the tongue gently.
It has nothing to do with the hitch ball.

Thanks for the tip. I will try this next year when I start towing the
boat.

If you are using sway bars (like a Reese Hitch) between the tongue and
tow vehicle, be careful not to put too much tension on the sway bars as
they will prevent the tongue from telescoping in on itself.

The trailer doesn't have sway bars (it is a basic small trailer).
Therefore, I don't need to worry about this.

Jay Chan