Rattles near the back of the engine compartment at low to moderate exceleration when engine is cold and at low rpm. I drove car with mechanic, who heard the noise. Dealer retorqued bolts, etc. on day one, but couldn't replicate problem. Kept car overnight hoping to replicate noise when engine was cold - they couldn't do it. I started the car next day and drove it about 6-8 blocks when I stopped at a stoplight. Car made noise at acceleration from that point on. I called dealer and explained this to them, but they still don't know what to do. What could be the problem?