Router has died. Need Advise Please.

[JAZZCNC]

However I was getting a lot of spurious e-stops and when I disconnected the earth strap from the machine and essentially relied on the spindle to VFD earth they went away i.e. my machine is only earthed at one point in the VFD whilst all the stepper cables are only attached at the control box star point.

This indicates you have some issue in some other area on the machine or in control box as doing this as just side tracked the problem not cured it.
Noise is a bear to find You could try taking a earth wire from the spindle body back to Earth on the VFD this will ensure the gantry is earthed at least and probably the rest of machine if bearings don't isolate the rest of frame but still not create earth loop as it's not connected to Star point in control box.

Have you measured frame with a meter to see if it's putting out voltage.?