yea me too. yea automatic, checked out bottom side today and all looked good and did some checks with it on the lift and in gear sounds like to me that its somthing making motor run rough and its making the exhuast vibrate making the y pipe make a hollow vibrating noise

 

knock sensor?

 

is this motor 3.4 v6 internaly balanced or external?

 

find your knock sensor (could be two on your car)and make sure it or they are pluged in. if they are plugged in and look good then unplug em one at a time and see if it makes a difference. if no difference in the way it runs then the sensor is bad or the wire is bad or the connection is bad. sensor or sensors should be on the side of the block below the exhaust manifold.