Loud bang when opening front passenger door

[SaggyCheeks]

I have a 91 Lincoln Town Car Executive series, and I went to school without the remote or door key, and I locked the doors. A security guard used a slim jim on the front passenger door unsuccessfully, then tried it on the rear passenger door, which he opened. Now, when I open the front passenger door, there is a loud bang coming from inside the door.

A couple of times it was hard to open; opening only about 1/3 of the way. I had to close the door, and try to reopen it until it didn't stick.

What could be causing the problem?

[YellowFly]

Check the clearance between the door and the fender. The door is likely "pinching" against the fender as the door is opened.