I doubt there is anywhere inside the M25 that isn't.
Routes are published by all kinds of bodies, probably Heathrow among them, but IMO you would have to visit places to see what you make of the noise, and compare it with the noise from buses, trains, emergency vehicles, parties etc etc etc to see what you personally make of it.
Heathrow also publish recorded aircraft noise levels at assorted locations.
Look at these pages:
https://www.heathrow.com/company/local-community/noise - there's probably enough information to keep anyone busy for a day.