Talcum powder in the joints.

The only real cure is to rip up the Wheatabix and replace it with proper floorboards.

We're the same. Guy who just put new bathroom in for us put a 'floor over the floor' = rock solid and no squeaks. Don't think tinkering with extra bolt-it-down will cure. We've a real bad on on the landing and then 1st step down !!!