2006 SV6 Jerking

I was reading through the threads and I noticed a similiar problem to mine was posted back in 2005. There was never any resolution posted. The problem is as follows.... I just bought a 2006 Montana SV6, and it has less than 500 miles on it. I noticed with the transmission in drive, brake applied, vehicle stopped, that when I release the brake and slowly move forward without pressing the accelerator, the vehicle will jerk slowly foward. It is very noticable. When I press the accelerator the problem goes away. I have taken it to 3 dealers and they all give me the same answer " this is nothing to worry about". I don't believe that this is nothing... it does not seem normal. I would like to know if anyone else has experienced this. The problem seems to be less noticable (although still there) if I have driven the vehicle for a while.