Car makes thump sound right after starting?

Question

I have a 2004 Cavalier. When I start the car, almost immediately after it starts up there's a thump sound. Just one thump and it seems to be coming from the front driver's side. No other time will I here this noise or other strange noises. I have the oil changed regularly as well as the coolant. The tranny fluid was changed after I bought the car in April 07. The check engine light is super sensitive and doesn't even come on for this.

Answer 1

the car could still be under warranty. the noise could be due to an engine mount that is weak or broken. the torque of the engine turning is allowing the engine to shift in the confines of the motor mounts restraint, but still making contact with the frame. after that i am not sure given the details.  

Answer 2

It may be a door or flap that redirects the air flow under your dash board. try starting your car with different settings on your heating controls and see if that helps.