Actually, if the key is starting to hold on it is something to worry about. Next thing you know it will one day just start running on while he is driving and pole itself to pieces.
hammer against the solenoid is not the trick to getting it going either, that is with low brushes and you tap near the brush plate on the com end of the field housing..
i am an auto electrician, i see people make the same mistake all the time and bash solenoids and break them for no good reason..