Hello !
 I'm facing a strange problem, which I'd like to describe here...
 My setup:
 - Chinese 2.2KW spindle + VFD, connected to Mach3 via ModBus adapter and Huanyang VFD controller plugin.
 - 3 axis. 
 - I'm using the famous Screenset 2010
 For example: 
 1st case:
 VFD Controller is configured to be started manually (Huanyang RS485 link is NOT used)
 I have to configure PD001 = 0 to run it manually
 I move all axis, alone or together manually ==> No problems 
 move axis, then start or stop spindle  ==> No problems
 You can play as you want, it's OK !
 2nd case:
 Now, PD001 = 2. Then spindle has to be started from Mach3 itself.
 (I click a button a the screen to start/stop spindle, or a command in gcode is triggered)
 Start Spindle, move axis, stop spindle   ==> No problems
 Move axis then Start or Stop spindle while keeping my finger on the direction button 
  ==>
 The stepper makes an horrible noise, as if the pulses received were totally wrong ! I have to release my finger from the 'move left/right' axis key, then press again and then it will be OK....
 Order is this case IS important ! YOU CAN'T start or stop spindle if an axis is moving !!!! 
 You will lose huge number of step, then you'll have to recalibrate and you work is lost !
 I was suspecting some shielding problem, but it's not the case (See 1st case)
 3rd case:
 The funniest case now:
 I disconnect the spindle from the VFD.
 Same test:
 I move one axis, then I start the spindle (While keeping my finger on the 'move axis' button)
 Same horrible noise !!!!
 I highly suspect a software problem (Or configuration 

? But I don't see where !)...
 Something look to 'eat' CPU, preventing a steady flow of data going to Stepper controller...
 Mach3 send a 'steady' amount of pulse to the stepper controller, then the stepper itself...
 But when I trigger the 'start spindle' or stop spindle command, it's a nightmare.
 I have to release the move button, then start or stop spindle.
 I have wasted a great piece of artwork that was under 'gcode' control.
 Problem: I cannot 'patch' my gcode files to ensure that no start/stop of spindle will be made while an axis is moving. 
 I have read plenty of forum, and each time, the problem is noise related. But trust me, it's not the case !
 Hope I was clear... Could someone help me ?