How to reduce noise in Control Electronics

Dear Sirs,

We have got Siemens 802D SL CNC controller wherein axis movement is erratic

Like we got a 2 axes Turing machine v replaced ballscrew, end support bearings, external encoder on the shaft of ballscrew, lubrictation is ok still suddely we find vertical axis has come down by 150 microns causing scrap. When we check repeatability of axis by using dial in Automatic program for 50 cycles, we find it to be ok and repeating but only during cutting, suddenly X comes down

We also checked alignment between self centering chuck center and tailstock

Please let us know what needs to be done to ensure there are no noises in Control Electronics

Is there any way to check/measure Electronics noise which can move axis (like drift) due to which machine not be moving as per command from CNC

Warm Regards,