Stepper grinding randomly

Hi All - I know there are about 100 topics here regarding stepper grinding, but this one has me puzzled. I have a recently converted machine using Automation Technology KL-8056D drivers, KL-DB25 breakout board (parallel port), all running through Mach 3. I can get the motors running smoothly on the table, but they will suddenly start to act funny. I've tried messing around with the wires, that doesn't seem to do much. I'm not sure if it's a setting on the stepper driver, or an unstable parallel port. I put a ran a program on it to show how intermittent the problem is.



https://youtu.be/b5CHwAnDChA

looks like the signal is getting interrupted inbetween. I am no expert but are you running other process on the pc? This may cause interrupts.