I changed the drivers door window regulator today as it was making an awful noise when fully open as the motor cog was jumping on the cam ratchet semi circular wheel. The root cause I discovered was the main pivot point had worn out even though greased and had about 1/8" play in it. This creates the problem as the window motor relies on the resistance only to cut out at the end of it's travel in both directions so it was overrunning cam ratchet semi circular wheel. So, if your window is making a 'chattering' sound when the window is fully open it's more than likely the regulator is scrap. Not bad really as mine was the original window regulator of 11 years old now.

PS. a new non OEM window regulator costs about £16.50 or about $28.00. well worth it not to mess around trying to fix it.