As an experienced custom house builder, squeaks are caused by the sub framing shrinking away from an attached member because of high moisture content in the sub framing leaving the fastener not snugged down to the framing.. Then, the plywood slides up and down on a nail shank causing the squeak. Pops are because the plywood was glued and the shank of the nail is not snugged down.When weight is applied the plywood sinks into the glue causing it to stick briefly and then once the weight is removed it pops back up fom the glue.
The most common call backs in custom homes are from floor squeaks. I have moved away from nails and go only with screws to help prevent sqeaks and pops because for some reason wood doesn't seem to shrink away from screws as opposed to nails. When gluing down and screwing off a floor I find to never add glue to blocks or add glue and a screw to prevent the pop. Screws need to be installed about every 3 inches to prevent squeaks . If you go 6 inches, which is industry practice, you will get squeaks. I wish they made floor screws with threads all the way up the shank of the screw but when made this way you get screw head failure because the threads cause a weak spot right under the head. Most floor screws now have a bugel head and a smooth shank.so, to really prevent squeaks you must sink the head below the first layer of plywood. Penetration of the first layer violates building code if the floor is a shear panel. I'm guessing threads up the shank too wont pass as a shear fastener too because of the weak head problem.
I'ts hard enough preventing squeaks in a stationary house... I can't figure how they expect it in trailer or motor home. In my first 5er, a Jayco, in a single printed add containing building points on a Jayco they guaranteed no squeaks, and put it in bold letters. When my Jayco developed a squeak I called them and asked their service department about it. After all, I have to go back and fix squeaks in the homes I build. They were shocked to find out about their own add regarding this and asked me to fax it to them. I did. Jayco apologized and eventually paid to have the squeak repaired but in subsequent adds that specific guarantee was removed. Apparently their add never filtered down to their customer service department because they called advertising and said no more on squeaks after that.
Try adding more screws through the plywood if carpeted. If another covering is down it will have to come up to add screws or perhaps they can be added from the underside.
-Paul R. Haller-