Use talcum powder if you have polished floors, as it is supposed to lubricate the joints. In the past I have used an impact driver and counter sunk screws to fix the squeaks before I put a floating floor down. - Brad
I had the same problem years ago and talcum powder fixed it right up. They never squeaked again. Make sure you apply plenty and brush it into the gaps. - Prof
Removing existing carpet to investigate squeaky floor boards is an involved process. If the carpet is removed or temporarily peeled off you need the right tools to relay it. If you do, it’s a matter of process of elimination, by walking on the board without the carpet and finding the squeaky area.
Once found, simply drill in some drywall screws to secure the loose board. Remember to drill to the frame and not just into the squeaky area. Walk over it again to make sure there are no more squeaks. Then relay the carpet. This is a common symptom of timber houses due to the nature of the material used. Sometimes we have to live with a squeak. - redracer01
I also learned that squeaking may be because they used nails to fasten the boards and using screws might grip boards firmer and less or no squeaking. I haven't tried that though but it makes sense. - folubode