I THINK I FIXED MINE TODAY. STEP 1 -- I MOUNTED A CONNECTION BLOCK ISOLATED FROM THE MACHINE FRAME. I RAN SEPARATE GROUND WIRES TO IT FROM; #1 THE SPINDLE FRAME #2 Z ASSEMBLY (THE SPINDLE IS ISOLATED FROM A PHYSICAL GROUND BECAUSE OF THE NON CONDUCTIVE RAIL GLIDE PADS). #3 THE BRIDGE. #4 THE FRAME OF THE CNC MACHINE. STEP 2 I ADDED ANOTHER GROUNDING BLOCK ON THE WALL NEAR THE MACHINE'S POWER OUTLETS. I CONNECTED THE GROUNDS FROM BOTH 220 VOLT FEEDS AND THE 2 DEDICATED 110 VOLT COMPUTER SUPPLY CIRCUITS. ALL 4 GROUNDS ARE CONNECTED TOGETHER AT THE BLOCK. THEN I CONNECTED THE MACHINE GROUNDING BLOCK TO THE WALL GROUNDING BLOCK. NOW ALL OF THE INPUT POWER GROUNDS FOR THE MACHINE ARE TIED TOGEHER ALONG WITH THE NEW ADDED SEPARATE GROUNDS. -- I THINK THE HIGH FREQ. SPINDLE EMITS RF THE BLEEDS INTO CONTROL WIRING AND PLAYS WITH THE ELECTRONICS IN THE CONTROL BOX. GROUNDING AT THE SOURCE OF THE RF ABSORBS / DISSIPATES THIS ENERGY. - I HOPE THIS HELPS YOU