No penalty.
Rule 13-4 c allows the player, to place his clubs in the Hazard, before he makes the stroke:
1. Provided nothing is done that constitutes testing the condition of the hazard or improves the lie of the ball, there is no penalty if the player ....
(b) places his clubs in a hazard.
Decision 13-4/21 rules on a case, where the player throws a rake into a bunker that
Placing a rake in a bunker is permissible. In this case, throwing the rake into the bunker was the equivalent of placing it.
We can learn from that decision, that the ruling bodies think, that the information, You could get from watching the rake fall into the sand is of no importance.
So throwing the club into the bunker should be treated alike.
McFade