I got my Santa Fe GP7 and was able to give it a good testing this weekend.
I experienced many of the same issues others have:
First, my engine made a scraping sound going in both directions. The cause of this was the wires to the front head light resting on top of the fly wheel. Pressing these up into the roof of the short hood fixed that.
Second was the grinding noise made when going around curves. This was being caused by the fly wheel rubbing on the inside of the shell in the short hood. I took my dremel to the shell on both sides to create a little more clearance. Noise is gone now.
Lastly gear noise. I have noticed a trend on the last few new Lionel locos I have gotten. The worm gear is dry with no grease applied from the factory. I greased the gears and it improved the gear noise, but it is not completely gone.