Hi Peter,
Yes metal web posi joists the builders cut hatches in the flooring which has created more creaking and clicking noises.
The flooring is moving quite badly upstairs and bounces when not even jumping shakes the wardrobe and drawers etc. (I'm not saying it should be solid and not flex!)
One carpenter has quoted to lift the floors and when i asked how he would do that he said cut around the stud walls!! I know the floorboards don't look fitted correct some appear to not have the glue and looks like they used ring nails which some have missed the joists below!
His suggesting the following
Take up floorboards
Replace and fit with correct glue
Take down ceiling
Clip up loose pipes
Raise Joist
Re board and plaster
Thanks