choppy running at slow speed

[nik_n_dad]

We have a small railbus that we've installed a NEM651 decoder into (soundtraxx 851001 MC1Z102P6), a nice, small cheap decoder.  At low speeds, the railbus has what I'd call "chattering" and runs rough.  If we push the speed up, it runs nicely, smoothly and quietly.  I've never delved into all CV settings beyond address, directions and lighting effects.  Any suggestions on things to try?

 

TIA

[KenS]

I don't have experience with any of their decoders, but the manual has a section describing their "hyperdrive" (high frequency PWM, what some call "ultrasonic" operation).  It suggests that some settings of this can produce irregular motor operation, and there are instructions on how to fine-tune the settings for an individual installation. From the description, it sounds like this might be something worth trying out.