I am having this same problem, but it sounds like a hollow clunk and it only happens when you hit an incline at an angle or a bump only with one tire (if that makes sense... it doesn't happen when hitting a speed bump with both tires). Is this the same problem you all were experiencing?
Did you ever get this fixed? Mine is doing the exact same thing. A hollow clunk when hitting an incline at offset angle or the right bump at slow speeds.