My was very tight in the beginning, after one summer of up and down, you can work on locking the roof in without making the "bang". It's really not all that good for the car and the top, to keep on doing that. Try and work out a way so you can bring it down more carefully. I can close mine with nothing more than a small touch, turn the handle and lock it in place.

Work on it some more, you'll get it so it doesn't bang when you close it.