[Gary]

Does it emit this sound when the loco is stationary with power applied?

I want to discount the track.

Assuming that it is a powered bogie of course!

If it does then the easiest thing is to take the loco body off and investigate further.

It might be that a worm gear and a worm wheel turned by it are not perfectly married up creating stress between these two gears which reveals itself in the form of this sound.

Happy modelling
Gary

 

[Gary]

One tip.

Carry out all maintenance work with your loco in a shoe box. No lost parts then. Springing rubber bands might be an exception though.

Happy modelling
Gary