Passat makes a "thud" sound??

Hi,

I have a 2000 Passat GLX V6 Automatic. When accelerating fast from a full stop, I hear a "thud" from the front of the vehicle. The sound occurs once when the car starts moving. If I accelerate slowly from a full stop, then I do not hear that noise.

Also, if I accelerate with my foot on the brake, I can create the same "thud" sound.

Any ideas on what that could be? Would this be something typically covered under a power/tran warranty?

Thanks, AABob