I had this issue, it wasn't hitting the idler bracket, but it was bowed enough that the eccentric spacers couldn't be tightened enough to hold the bed stable and it would wobble. I also started about a week after I finished putting the printer together. I emailed Colin, an he sent me a new bed the next day. Its been about 3 weeks since I installed the new bed and it is fine so far. The baltic birch plywood ought to be pretty stable against warping, but there must be the occasional bad batch.