We are about to begin installing a floating engineered wood floor, however after ripping up the carpet we realized there are a few soft spots in the floor. These spots were not caused by water and are impossible to get to from below due to a finished basement ceiling. We tried using 2 1/2" deck screws around the soft spots which helped, but did not fix the problem. What issues will we run into if we leave the soft spots and lay the floor down. And if it will be a big problem, what is the easiest way to fix it without ripping up the basement ceiling? Thanks for your help!

Maybe pull the sheets of ply or what ever it is.

Tammy,
Drill a few small holes thru the subfloor (I use a 1/8 - 3/16th for that to prevent the drill bit from breaking easily) next to eachother in a line where you expect the joists to be and mark the joist with a magic marker, do so on both sides of the area/room and snap a chalk line over the center of the joist. Now you can screw the subfloor down without missing the joists. That will take the squeeks out for sure. Go around the whole room and correct any of these squeeks/loose subfloor.

Johannes.