It will also depend on what part of the tree they are working on. If they are down on the ground you may only hear them pull off the bark. If they are up in the tree then you may hear the commotion of climbing and pulling bark.
If you heard activity, and it was a bear, then it more than likely was stumpin' for bugs and grubs. This can often be heard a long ways away. One time I heard a bear pulling long slats off a cedar log and you could hear the cracking and slapping from 200 yards away.