I have one of those dual motor Athearn DD40X engines that I put a DCC decoder into. Yes, it makes the typical Athearn growling noise and there's little you can do about it. I just regard it as a cheaper sound system than what a decoder would cost.
How long have the loco's been run?
There's a few threads where people use pearl drops tooth polish to smoothe out the gears. Run with the pearl drops for a certain amount of time, then clean them out and lube.
Springfield PA
I have 2 Athearn EMD DD-40X Two motor locos which I have restored but as with all older Athearn motored units I cannot get the excessive drive train noise out. Does anyone have any suggestions or do I need to remotor with newer drives?
I have lubed all gears and have also cleaned the armatures with a bit of lube and the end thrust bearings but still noisy. I would like to add DCC sound but pointless.