So I re-seated the drawbar connection to the tender, checked and exercised the DCS and 3-Rail switches on the tender. There does not seem to be any roller/pickup related issues. Runs fine on the test loop.
Unfortunately no improvement. I have throttle response, smoke, background engine sounds. No chuff, no coupler clank, "chopped" whistle blast.
The fact that it is a new $1k locomotive, I am not inclined to open anything up...
Any last thought before I contact MTH?