Ausie.......you are right some risers will not allow you to get the shelf exactly tight against it. If ZE shelf is truly flush against the riser it shouldn' t make a peep. In the case where there is an unavoidable gap, get it away far enough that it has no chance to vibrate into the riser.
A layer of moleskin along the edge before you snug the shelf up tight to the riser will help as well.
Also moleskin the entire hook arm along the top edge from the tip to bottom(a 1/2" piece as long as the hook tapered slightly for the tip itself)......then take a razor blade and cut down thru the moleskin into the " V" on the hook. Press the moleskin down into this " V' to define it............ you won' t hear ANYTHING when you draw.