Are pre-engineered floor joists (silent floor system) made so that there should not be any squeaks, hence silent. In attempting to solve the "crackling" sound coming from my lino floor, my builder has pounded in shims between the subfloor and the pre-engineered joists.Of course this did not work. Now they created a squeak in one area. Wouldn't these shims lift the subfloor slightly off the pre-engineered joists, since they are supposed to be made completely flat and are not warped or curved like ordinary joists? Is it normal to use shims between pre-engineered joists and the subfloor. I am afraid that the builder did more harm than good. Will these shims affect the floor?