I would recommend having a look at the strap (door check, actually). The most common failure is when one of the ball bearings (there are several in the mechanism) gets loose from the indents and the door gets noisy or sticky when opening or closing. You'll need to pull the interior trim off the door and then carefully lift the door card out so that you don't break the plastic hooks on the inside of the card. If you do, a glue gun will reattach the hooks.