We are having the same issue in our 6 month old house, initially this work was done to one room which hasn't stopped the cracking noise from below:
Removed old flooring which had been glued and nailed to timber joists. Joists are at 400mm centres and have staggered noggins nailed in the centre of the span from wall to steel RSJ. Joist length is approx 4.1m
Re screwed noggins as a precaution with 100mm x 5’s.
New boards down and glued with egger D4 glue as per manufacturer instructions, the boards are also fixed with 75mm screws on every joist, 3 per joist.
Glued and screwed a noggin to the perimeter as needed.
Where the boards cross the steel used gripfill green so the boards are not directly on the steel.
The warranty holder Homeproof (was Aedis) have now backtracked and said the Developer doesn't have to do any remedial work as it not covered as 'Major Damage' in their policy so they and the Developer are not liable.
So if we have to do the work ourselves has anyone tried the NHBC fix as per the joint statement? How much does it cost per room and how long does it take in terms of disruption etc and had it worked? How do we find someone who knows what they are doing as well?
I know I am preaching to the converted about the scandal of the lack of protection for owners of new builds.