Hi I got an 2008 cts all wheel drive (cts4) 3.6di the problem I have is when I acelerrate if I do it normally is OK and could keep accelerating with no problem the problem is if I'm at complate stop an I accelerate metal to the peddle quick acceleration i hear a loud and ugly sound underneath right at the middle of the car like loud grinding gargle goes away if i let loose a little the gas .