VHD Mounting problem

[PWD]

Hi wonder if anyone can help. I bought a CNC router from a chap a while ago now (about 5 months ago). Anyway have just started to set it up...when I bought it the guy advised me the VFD should be mounted as far away from the router as possible as it causes interference. Anyway mounted it about 7ft away from the mill which isn't as far away as he had it but due to the cable length/run around my workshop walls this is as physically far as I can get it. OK now if I turn on the mill without the spindle/VHD on everything works fine...however turn on the VFD and things start going awry...the stepper motors start making a grinding noise and creep the whole rig around in small steps. So is this correct is the VFD causing interference and if so I need to move it further away, which means buying a new length of cable...so which cable do I buy, is this any use. Many Thanks in advance.
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