Hi John,

This could be one of a few things.?
1: It could be a lose coupling which is slipping ever so slightly.
2: Missed steps either most likely thru over tuning.
3: Electrical issue's either thru lose or faulty wiring or interference noise/bad earthing etc (possible bad drive thou unlikely)

First stop is check couplings etc, use witness marks if possible to easily see any slippage.
Check for lose wires etc.

Then and probably the cause of the problem look to the motor tuning, esp the acceleration.

If you could give more info on the system it will help greatly. Things like.!
Drives model and micro stepping used.
screw pitch
voltage running
BOB model
Mach motor tuning settings: . . .velocity setting, acceleration, steps per, step pulse, dir pulse.
Shielded cables or not.?
Is Star grounding being used.?

Does it look to be just in 1 axis direction or more than one.? If so which.?
Is the wavy stepping a side ways consistent step over or wavy in and out.? up or down.? Pics would help.