Can you duplicate the noise by racing the engine in park or does it only grind or rattle when the in drive and accelerating? Noises are very difficult to diagnose in this type format because I cannot hear the noise your description and potential location of the noise can be very helpful in isolating the problem.
There a couple of things that can cause this rattling type noise on acceleration the most common was the serpentine drive belt tensioner there was a service bulletin to address this. That bulletin number is XXXXX The other problem is with the heat shields on the exhaust have a tendency to rattle also. I would have your local mechanic inspect both of these issues have them pull the service bulletin to verify whether not yours has been replaced or is making noise.
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