Flooring – Floor panel bulging up

We are assuming here that the noise is caused by hard shoes on a hard surface as opposed to a structural defect that causes the floor to creak or snap under the weight of foot traffic. I think you are on the right track here. If you want to stay with a hardwood type floor, as opposed to carpet or vinyl, There are several sound rated underlayments for use under engineered hardwoods. Please, don't say the word laminate flooring or we will not be friends!!! It is not unheard of to use two layers of the closed cell foam backers. An alternative that might be a good compromise solution is vinyl plank or foam backed vinyl flooring. There are some very good looking vinyl products that look very much like wood or tile. I have been using a foam backed vinyl sheet product from Tarkett in many of my apartments that looks so much like real tile, folks have to get down on their knees to check it out. The nice thing is that my cost is only around $1.00 per square foot, a bargain. Some of the new vinyl plank products look more like real wood that real wood does! The last suggestion is to ban shoes in the house and issue soft fuzzy slippers to all residents!

I have seen 3/4" thick hardwood floors go over 1/2" subfloor with no problem. Your floor structure is plenty heavy to carry any load you apply to it. In many older homes (really old homes) there was no subfloor at all, and the floors held up very well.

Remove the layer of MDF, clean up the nails, and reset all the nails that are in the subfloor. This minimizes the chance of squeaks from the nails that may have risen up as the framing dried and shrunk. Add 1 5/8" screws at all the edges and 3 or 4 more spread across the center of the spans of all the plywood.

In my humble opinion, DO NOT use an underlayment foam under hardwood flooring. This is only intended for floating floors!!!!. The "give" the foam has, is asking for your floor to squeak!!! The only vapor barrier you need is a 5 lb. felt paper. It is much lighter and much thinner than roofing tar paper and will give the resistance the wood needs against moisture rising from below. This is what is used in all new floor applications. Sometimes, on occasion red rosin paper is used too, I believe it is error, it has no resistance to vapor permeability.

After this initial bit of prep, lay your new floor.