Starter

Hey guys,
I have noticed after installing my new Summit Protorque starter that when the car is at normal engine temperature and i try to start it, that it makes a brief noise like it stays engaged a fraction of a second too long??...(this noise does not occur when starting the car cold)??...Any ideas about this noise?? Thanx

The starter did not come with shims, but has different mounting holes on the backing plate for oil pan and header clearance...