You can't do it really (that i know of) because the physics stuff is embedded into Box2D. That's not to say you can't do it yourself. It's mostly just checking a couple of variables rights?
Object1 On Collides with Object2
Object1 Speed
Object2 Speed
Object1 Density
Object2 Density
if your char has a max speed of 500, you can just say, if between 0-100, and collides with something, make sound 1, if 101-200, make sound 2 etc.