Requires Unity 5.0.0 or higher.
Bring your physics to life withPhysSound!
PhysSound is a system for playing audio based on physics interactions between objects, greatly increasing the realism (and satisfaction) of Unity's physics.
Guide & Documentation | Demo Support Thread
Features:
-Impact and Sliding sounds.
-User defined material types that allow unique sounds to be played based on the kind of object hit.
-Ability to play different sounds based on the impact force.