One thing I learned while looking at 'noise abatement' procedures was somewhat counter-intuitive. Specifically, doing a derated takeoff didn't reduce the noise footprint - it actually made it larger (there is a db limit that defines the 'footprint', although I don't recall what it was).
What happens with a derated takeoff is that you make less noise, but you spread it over a larger area because you climb slower. So the peak noise goes down, but the 'noise footprint' doesn't reflect peak noise - just the area exposed to the noise level above the footprint threshold.