An interesting point here: there is no limit switch telling the motor when to stop. When these metal pieces come into contact with its housing, the motor can't spin anymore and will draw more current to attempt to keep going. Only then does the circuit stop powering the motor.

If the lid does work correctly on your unit but makes a ticking sound, this may be because the set screw is just a little loose, so the motor isn't able to find a definitive stopping point. It then doesn't draw enough current for the circuit to stop powering it fully. The motor's attempt to keep going can also further loosen the set screw.

This is not the most robust design, as this is what causes the set screw to loosen. You'll have to keep re-tightening it over time, and in extreme cases, this may lead to the motor housing cracking, or gears inside the motor breaking.