Very slight "Hiss"

When I press my ear next to the tweeter, either channel or input selection, I hear a "hiss". I have tried chokes, and changed physical position of IC's. However, I noticed that if I select an input that has nothing connected to it, the hiss increases. The hiss is small, but it really bugs me all the same. Might there be a way to eliminate it??
Thanks.
Rpg