How do I reduce noise from the bolt hitting the strike plate on a door with an automatic closer?
One of the adjustment screws is for the swing speed, and one is for the latch speed. It sounds like the latch speed is too high.



Adjust the latch speed until the door is just moving fast enough that it closes. You'll also want to be sure to test it by opening the door the minimum amount someone would open it. 

If it doesn't shut if you slow it down at all, it may be the door arm is installed incorrectly. 

If it doesn't really slow down when you adjust it, then it could be the closer is broken (lost fluid or broken valve seal) and easiest thing to do is replace the entire closer.