Crosstalk between water cooled spindle and endstops immediately when starting

Hi,

a friend of mine has build a cnc that uses the "default 2,2Kw water cooled spindle" that is availabe on ebay.

Now there is the problem, that as soon as the spindle is started the endstops of the cnc are triggerd.
The spindle is not yet connected to PWM or something so its just the speed-control-inverter plugged in near the cnc.

As soon as the spindle starts (also very slow) the endstops of the cnc are triggered.
If it is plugged in a power point a few meters away at the wall it gets better but still sometimes triggers the endstops.

First I thought it might be because the endstop-wires are not shielded but even moving the spindle far away from the wires does not help.

The wiring of the endstops is as described here: linuxcnc.org/docs/html/config/stepconf.h...witch_wiring_options with the "Normally Closed Switches"

There are no pullup resistors at the moment but I do not see how this could lead to a false positive with the "Normally Closed Switches"-wiring.

Do you have any idea what could be the problem here?
Cosstalk trough induction over a distance of 2m (that is what we have tried) seems a bit far for me) or some ground-lifting problem over the powerline? Or something else?