I'm getting this knock noise (just one knock) when accelerating in first gear. What could it be? I've dont some search and it could be a loose flange or a bad/loose rear motor mount. How do I know if the motor mount is bad jus by looking at it. It isn't the exhuast flange cause I've checked and it looks good. The motor mount looks ok also.. it almost sounds like something is loose and hitting up against the firewall of the car whe I accelerate from a stop and go in first gear only. let me know what u guys thing. Thanks