Always keep the extras at the bottom of your string. Even if they didnt help in sound absorption, and speed I would leave them. They could be very important, should your current button break or wear out during the season.

Fortunately for you, they can actually speed a bow up if placed properly. Weight at the ends of the strings CAN add speed. Sameas shrinkwrapping brass nocks at the end of a string. Check it through a chrono if you really want to know, and you can play with the positioning till they add or lose minimal speed.

Also, being they are rubber, they may absorb some sound, but I have no proof of that.