check those screws, and any other moving parts. could a piece of rock or something be caught in the mechanism?

If you decide to get a new pedal system, do take a look at Speedplay Frogs. No moving parts. Nothing to adjust. Lots of float. (of course, if you don't like float they will be totally wrong for you.) Yeah, they are mtb pedals and the fashionistas will roar, but who cares?