I lifted two runs of our creaky 1950s upstairs hall floorboards, which aren’t in great condition and had obviously been up before, to run in a cable. There is a sheet of 3mm hardboard between the boards and the underlay across the whole hall. They have now been temporarily replaced with the hardboard and carpet, without any fixings. And they no longer creak. Is it absolutely necessary to screw them down to the joists?