Hi,
the electrical noise is being generated by the speed controller and your spindle motor.
It is being radiated to your signal lines in your machine. They are sensitive. A big
noisy (electrically) motor running right next door will induce small voltages and currents in signal
lines close by.
You can jump up and down and blame Mach if you wish but it wont do you any good, this is
physics...you could blame James Clerk Maxwell (1831-1879), the 'father' of electromagnetics...
but hes just a little bit dead at the moment!
Good practice put all the high power lines like your spindle wires as far away from Machs signal lines as possible.
The next best practice is to put filters on the input and output of your speed control. If you have
a VFD you MUST follow manufacturers recommendations or you will blow your VFD up.
Your speed control is very much less high tech and good line filters will help a great deal without risking
your speed control.
The next technique is to reduce the sensitivity of the signal lines to electrical noise. If you have a look on
the ESS Config plugin, Pins page you will see that inputs have a filtering setting. Try putting a setting of 100
say in each of your limit switch inputs. It may help.
Best practice is to prevent your speed control generating noise ie line filters, next best is reducing the coupling
of noise into your signal wiring, ie physical separation and screening, the next best is introduce filtering on the inputs,
ie the software filter I've mentioned and/or RC low pass filters on the pins.
Craig