We've noticed an increased noise nuisance from Heathrow departures in the Woking area recently; they seem to be climbing slower than they used to especially in the evenings so although they appear to be using reduced power, to the human ear the noise level is the same so we're exposed to the noise for longer than we used to be.
Would this be due to ATC not cancelling the speed limit like they used to?
No. People are finally becoming wary of TCAS RAs and respecting the guidance to reduce the rate of climb/descent to 1500ft/m within 2000ft of level off. Unfortunately some people are very keen and will drop the rate to 1000ft/m going through 2500ft altitude, hence more noise.
We've been forbidden for asking for high speed for years, IMHO it's up to ATC to offer it if they want us out of their sector.