Greetings, I have a 2 story house that has had a popping floor all over the place. I am thinking of turning the basement into a suite but I can see that after a few months of the popping noise from above, the tenants will... well, they wont be happy. The subfloor is the simple plywood on the trusses and nailed in. The basement ceiling is unfinished (and I am putting in a drop ceiling, not insulation with drywall). I know the majority of you are thinking that this is a nail rubbing issue and it very well could be; however, here is the kicker: The last time we got new carpets, I spent a good 30 hours screwing the plywood down beside all of the nails and at the same time, removed the old nails that were removable. This fixed it for about 6 months but after a cold snap and the warmth of spring, it started up and is just as bad as before. What are your thoughts on hammering in shim between the tresses and the sub-floor (from the basement) and filling in the slightly raised crack with construction adhesive, then trimming the shims... kind of like this....: http://www.monkeysee.com/play/19867-fixing-floor-squeaks-from-the-underside ? I am open to many ideas without having to remove the carpet or sub-floor. Thoughts?