Before I bought my 05 6cyl I drove two others. They both had a driveline thunk between 2nd n 3rd. The one I bought didn't do this then but shortly after I bought it of course it started. My car has 46000 miles. It seems it only does this 20% of the time and only between those gears. Feels like the whole driveline moves. Is this commen? Caddy says its normal of course. Its very noticeable and embarassing. Thanx in advance.