I don't know how safe your set-up is...But If you power up the machine only, no computer ,no Mach , does it still do it? (Dont attempt if you know the machine will run away uncontrollable with no controls on it! I dont want you to get hurt or damage the machine)
BUT..Then you can rule out anything computer or software related, that is...
If you are getting power leakage to the drives before the "automation" or control takes over the machine.
When you say no movement is seen on the DRO, Do you mean the MACH screen, or do you have a seperate DRO on the system?
The fact that you can hear/see the x axis moving, (when no control is asking it to move), is probably the reason why you see no movement on the DRO. If you had encoders you would see the movement coming back to the DRO.
If you are also seeing all the axis creep now when no control command is given, I would look at your power set-up/ gains ect... you also mentioned that you are missing steps during a run, which could mean the controls are having a hard time positioning the axis due to the fact that the drive(s) is not set-up 100% or the power going to the drives is too "Dirty".
Hope this makes sense?
I am out in Georgetown...where are you in Ontario?