Tighten them up as far as they'll go - do it carefully, as the end of the plate where the screw sits can break of you're cack handed. Then count the number of turns as you slacken it up all the way, then tighten it by about a third.
Check the cleats are mounted properly and level, and inspect them for imperfections in the casting. Even good ones can be a bit rough, but a careful stroke with a file cures that.