I have just started having a problem with my servo, with the machine plugged out and disconnected, the servo makes a terrible noise, when i plug out the cable it is fine, if i plug in the other axis cable it is fine, i have checked cables etc and they seem ok.
I have made a quick video of the problem.
First plugged in correctly, then removed, then with the cable of the other Axis.
Has anybody had any experiece of this.
Alan
Cannot tell much from the video (sound too weak).
Are you aware that spinning a servo will generate a voltage, and you will feel the steps as it rotates?
Thank you for the reply Mike, the sound is not very loud and is hard to grab with a camera, The axis is moving jerkily instead of smoothly, making a thudding sound, but only when plugged in, if i swap with the other axis cable it works perfectly, as normal. I have decided to buy a new motherboard as I presume this must be the problem, it does not seem to be the cables as I have checked them in different ways. Thank you for your time, it really is much appreciated.
If you plug the Yaxis cable into the Xaxis motor and it operates smoothly, then yes, it is on the controller board. Before you buy a new one however… 
Did you (if you can) switch the driver modules between X & Y? If the problem goes to the Ymotor, then the driver is bad.
Did you try adjusting the driver current adjust potentiometer? Too high or too low could cause the jerky symptoms you describe.
Did you check the GRBL Accel settings for X & Y ($120 & $121)? They should match.
I hate to hear you bought a new board when there could have been a much cheaper fix. 
Thank you so much, this is exactly the information I need, i will get busy with this. Your comments make a lot of sense. I will have to cancel the purchase quickly, and hopefully get it working. Thank you so much, it really is much appreciated.
Update:
I have checked the items that you mentioned. GRBL settings fine.
Unfortunately, since it’s an integrated driver, I cannot switch drivers or change potentiometers and I belive the fix is replacing the whole controller board. In a way I am happier to have a more hobby friendly board, so that I can learn more.
Thank you for your insight. With your help I now know that I have made the correct decision and not wasted my money. Thank you, much appreciated.
Glad to help. Just remember I am one of many helping on the Forum. They usually let me go until I run out of ideas, or make a huge mistake, then join in for support. Sometimes even the helpers need help. 
By the way, welcome to the Forum. You will be stunned by the wealth of knowledge thad you have exposure to. I saw no mention of Lightburn, so I hope that is one of your tools.