I purchased a new spectrum 8-40c about 2 months ago. It has been a great running and very low noise loco. Anyway I was gone for about a week and I came home the other night, started to use this loco and it makes a loud grinding noise in the front truck(under cab)all of a sudden. It was not moved from it's spot while I was gone. It is clean and has been lubed properly. I have taken it apart and I can not find what is causing this noise. The gears are tight, no chips in the gears, no debri in any of the mechanism's. Anyone have any idea what this may be? I have 2 others and they run just a smooth as can be. Thanks!