I noticed this on my printer as well. To fix it, you must remove the print bed (the glass and the aluminum plate) and the tighten all of the nuts that carry the V slot rollers on the bed carriage starting with the ones on the right hand side. There are standoffs under the ones on the right. Once they are tightened, tighten the 3 on the left hand side as tight as you can go or until the carriage doesn't wobble any more.
This drove me bananas until I figured out this fix.