Best method for closing the bonnet - pull the bonnet down until it has about 40cm before it would be shut, then let it drop. I was shown this by BMW engineers. It stops you pressing the bonnet and causing any possible damage/dints.
The 'catching noise' is probably just the bonnet catch.
make sure it closes right on both sides though. Had an alarm uninstalled from the car and when I went to pick it up one side of the bonnet was fully latched and the other was not. It has happened before to, so be careful.