I spent the last few days trying to solve our creaking chipboard floors. Downstairs and even outside, you could hear anyone walking on the upstairs floor. I searched the forums and tried out several solutions, but this is the one worked for me. Having screwed down the boards next to the nails, applied talc between joints and further screwed at 100mm intervals, the damn floor kept on squeaking. As a last ditch attempt I cut out a section of the floor near a squeaky section using a couple of pilot holes and a jigsaw (obligatory waring about pipes and wires). Here, I could see that the pipes and mains cables were laid against the plasterboard ceiling below (and therefore not at risk from cutting). Crucially, though a quick wiggle of the noggin (piece of wood perpendicular to and in between the joists) revealed the same hated squeak. I also noticed that in my situation the noggins were lined up although slightly offset along the length of the floor. So my solution was to fix back the cut out and drill, coutersink and screw 80mm chipboard screws down through the floor surface and into the offending noggin. A quick walk test and it was obvious that this cure could be rolled out along the entire upstairs floors. The remaining noggins were located by drilling into the floor at stategic locations - if the drill went straight through - no noggin, if the drill met resistance all of the way down through the floor and into the noggin - you had found the next culprit. I hope this solution helps someone out there save themselves a whole saturday of pondering! Thanks for other comments on this forum.