Ok just rebuilt my big printer and now I have this… anyone know what it is and what causes it
Well judging by the lack of comments I would say that nobody knows what was causing this. So the problem was a bad bearing in the y gantry. So there are 16 wheels on just the y gantry and this is what happens when just one gets a dead spot. Wonder what would happen if they all went bad. Needless to say all 16 are now replaced and it is printing like a dream.