gp9 drive noise

[thetramp]

I have an old athearn gp9 from about 1975. I pulled it out after about 30 years and ran it. It ran slow and would stop completely after about 4 rounds on a 4 X 6 layout. It ran very quiet. I replaced the motor and now it runs great but there is a loud noise ( seems like it is in the front trucks) when running forward. Seems like it make more noise when on a curve. When it runs backwards, there is still a noise but it is not as loud as going forward. The trucks and gears have been oiled and greased. What could be the problem - cracked gear may be? I don't know what to do. I though I should try changing the front truck assembly but I haven't found one yet. I don't know what but something happened with the remotor. I like this engine and would want to keep using it. Anyone have any ideas?