Watch not cleaned and oiled properly.
Hands hitting together, on face, or on crystal.
Hairspring not centered between regulator pins.
Regulator pins bent out of parallel.
Hairspring not level.
Hairspring out of round.
Hairspring pinned wrong.
Overcoil wrong.
Damaged or dirty jewels.
Worn bushings.
Balance pivots loose in jewels.
Balance out of round or flat.
Balance heavy on one side.