Sounds like the cog that is attached to the peg is slipping. if u look closely at the back of the machine head you will see this cog has a phillips head screw in it. Perhaps try tightening this. Also put say a very tiny blob of vaseline on the teeth. Although if u notice on inspection of this cog any broken teeth then... you need a new machine head.
Try tightening the screw on top of the machine head. Its usually very tiny (for aethestics reasons).

Merls