i had some mysterious noises quite the same as this one on two other cars (not contours) and they both happened to be faulty motor mounts. if the rubber part breaks it may cause the motor to sag and make a strange noise. you can eventually identify it by parking on a steep hill with either the right side up and down. if it´s gone in one position and apparent in the other position (with the car not moving and the motor at idle) you might have found the problem.
