DRO runs away when I turn on motor

[Briney Eye]

So, I'm not sure where to start troubleshooting this, aside from swapping out the DRO entirely.

This is on my lathe. Whenever I turn the motor on, the Z axis DRO readout starts rapidly increasing. I'm using the original iGaging linear scales, with shorter and shielded cables. The lathe uses a KB Electronics PWM. 

Here's a video of it in action:
https://youtu.be/Oc5jP8JfYJQ

Any ideas what's going on and what to look at first?

For me, the best solution to noisy/drifting scales was adding power supply decoupling capacitors in the scale read heads.  Transformer-type wall warts can help some, but the decoupling is really the solution.