The whole point of a floating floor is to allow for expansion and
contraction of the timber. timber floors will expand / contract about 2mm
per metre, ( in UK weather, may be more in more variable climes ) so with a
modest room of say 4m length of board an 8mm expansion is to be accomodated.
This can not be done by nailing the boards down and will result in the
boards lifting / twisting.

The creaking noise normally stops after a while, once the floor is " bedded
in"