Marx #898 loco

[ThomasB]

Thought I would move this here in hopes it may be seen more. It's been yrs. since I was on this forum, having given away my Marx trains to my grandson. I just bought a nice little set of Marx Streamline trains, post war, that was in half of it's original box. The engine is a #898 with a N.Y Central tender, a box car, tank car and a gondola and caboose. The cars are 6 in. tin with 4 wheels.It came with all the original track and the transformer. After a thorough cleaning of all the electrical parts and the wheels it's running great, except I'm getting sparking occasionally from the engine wheels if I run it alone, not when the train is hooked on. I'm also getting sparks at the couplers between the tender and the engine, not the other cars. I've never seen that on my other trains, any ideas? There must be current running up to the coupler somehow to make it spark. Thanks in advance. Tom