[34C]

I would want to tinker with the motor mounting, particularly to ensure the worm gear is meshing properly. A couple of years ago I bought two Hornby 8F's. Both ran very well as received, one was properly quiet, the other sounded like a coffee grinder. The motor and worm gear cover were not quite in a straight line with the rest of the chassis on the noisy one. A slight slackening of the screw holding the worm gear cover, realignment by eye, and retightening, and it was quiet. If it is not that, similar noisiness can result from a tight gear or axle in the drive train. With the motor mount slackened off enough to free up the drive to the chassis you can check whether it is the motor that is intrinsically noisy, or the drive train tight or binding in some way. As Rob wrote, if it is the motor it may quiet down with some running, but usually if they start out rough, they never become really quiet.