Aging
Aging does nothing to the sound of the coins.
Aging them darkens them so that can be distinctly seen. You darken or highlight areas of the coins and can polish or birghten up the raised surfaces of the coins so that light hits them a certain way.
Getting them slick is a whole different process but most people get them slick or soft to start with. a soft/slick coin will not talk when the coins rub accross each other and can be useful in many many ways.
Later,
Snorri