Creaking tongue-and-groove chipboard is a common condition with houses built since the Eighties. Chipboard is often considered unsuitable for domestic flooring, because it is an inherently unstable material which is bound to sag under its own weight. This causes the joints between adjacent boards to open up, and it is the edges rubbing up against each other that causes the creaking.
Unfortunately, despite thousands of complaints, this material continues to be used in most newbuild houses because it is cheap and easy to install.
By removing the chipboard and replacing it with proper timber as a sub-floor, you can have a much more stable base.