have you tried using a long weight?
the squeaking is caused by the treads moving up against the nails - over … the squeaking is caused by the treads moving up against the nails - over time the flexing of the wood causes the nails to rise up a tiny bit. You can bash the nails back in again, or use new nails in addition - but they need to be 'cut' nails that are flat on the sides. I've never heard of a foam or glue, but another temorary fix is to sprinkle talcum powder onto the squeaky area. Talc acts like a dry lubricant and stops the squeaks - works on floorboards too.