Im installing 3/4 hardwood in a house I just purchased. It has a 5/8 plywood subfloor. I just removed the 3/8 particle board underlayment and a layer felt between the subfloor and underlayment in the living room and master where the solid hardwood is going. The 5/8 subfloor feels a little soft where the seams dont meet with the joists. i want to put a layer of 3/8 bcx over the 5/8 subfloor. I was planning to use a layer of 15# felt between subfloor and underlayment to eliminate squeaks. Is this necessary?... all the sites ive searched have never suggested this but the particle board had it. Also one of the other rooms im putting 3/8 bruce engineered hardwood that was given to me. I havent removed the particle board in that room. Is it ok to put a layer of 3/8 bcx over the particle board and instlalling the 3/8 engineered so it is the same height as the 3/4 hardwood. Im stapling the 3/4 hardwood and planned on gluing the 3/8 engineered????