Rattle sound under car when accelerating

[Coldo489]

I have a 08 cobalt LS with 90k kms. When the car idles it is smooth and when you lightly accelerate it sounds normal. The problem occurs when you put a load on the engine or put your foot into the throttle upon heavy acceleration or going up a hill. It sounds like a rattling can or almost like a plastic bag is stuck under the car fluttering. Sounds comes from underneath the car. Has anybody heard of this? when in neutral and revved up there is no sounds from engine bay. just upon acceleration it does it.

Thanks

 

[YelloEye]

Sounds like one of the heat shields is loose. Check all the rivet spots along the exhaust tunnel.