06 rattle, transmission???
 

My 06 Malibu has a rattle when first pressing the gas pedal and only last for a second or two. It sound like it coming from the transmission. The sound only happen when the car is in drive. No noise in park or neutral. It sound like it might be the stall converter engaging. But the transmission works good otherwise. It could be something lose rattling only when the transmission engages.

Found out an exhaust shield was loose. Clamp broke. Put a new clamp on it, no more rattle.