Denford router driven by Mach 3, every now and then the machine loses position and there is a knocking noise on each of the three axis which s mostnotable on the X axis. Here is the noise https://lozharroplures.co.uk/my_images/Xaxis.m4a

I am pretty sure that it isn't a mechanical problem as all axis are affected. The machine can run for weeks with no problem even running non stop for 20 hours. Rebooting the PC and /or the control box doesn't help. The spindle is controlled with a VFD plugin.

https://lozharroplures.co.uk/my_images/1.jpg

Any ideas anyone?