Hempel Silic One and Hempel Alu safe

This year I try out the Hempel Silic One propeller kit which is a silicone based product for the propeller to prevent algae and barnacles on the prop. On the saildrive and on the bow thruster drive I use Hempel Alu safe. After a short trip on the water I realize that the propeller has a different sound at certain revolutions.