I have only purchased one of these so I can only speak for the one I own. That being said my SD-40-2 arrived looking good and functioning as expected with the exception of the wheel widths. All the wheels are quite narrow making the trucks loose in the tracks. The result is a rather noisy loco as it rattles around the track. Don't know if this is just mine or all the SD-40-2's. My other new Bachmann ES44AC loco does not have this problem.
The locomotive runs perfectly. The sound is very good in my opinion. The problem was, the rear coupler did not want to couple to any thing. I had to rip the rear coupler assembly apart. I crazy glued a kadee coupler to the rear now everything couples O.K. but it was a huge aggrevation, and I'm sure the rear coupler assembly will come apart down the road.