All I hear is the tenders wheels. Have you lubed the axles?
I don't think that is possible, because the locomotive is elevated and stationary in that video.
It does not sound normal to me. it sounds like binding in the gear train or something in the motor itself is not right. I would remove the motor from the chassis and apply power to see if the noise is in the motor. Don't disconnect the motor electrically or you will have to use a DC supply to power it. If is is quiet, then I would starting looking at the drive train for lubrication issues or a gear alignment issue. There could also be some other component that is loose and making contact with a gear. Just my take without actually having it in hand.