Officially, Heathrow's measured noise footprint is the smallest ever -
New report shows Heathrow's noise footprint at smallest recorded levels - Your Heathrow
A380s also measure quieter than older 747s, which, given that they are almost one and a half 747s, is pretty good.
However, the one thing I have learnt from 20+ years living only a couple of miles (as stuff flies) from an airport and nearly under flight path, is that annoyance is very very very subjective and dependent on an awful lot of variables. Older jets (so far as I can tell from my limited identification capabilities :-) ) are almost always louder, but it will also depend on engine type, load, fuel load (how far it's going), atmospheric conditions (not just wind), heck on approach the exact point the AT/PF decides to spool up can make the difference between lying in the garden with eyes shut wondering if that was a plane going over or not, and suddenly waking up thinking "thats a loud one". Military is typically louder still (that's big(ish) stuff, don't usually get fighters in, you probably don't get any mil stuff at all at Heathrow) - not just because it's older but also because they don't stick to the usual flight paths and it doesn't sound like they pay the engine mfrs every time they firewall the throttles either...
Ironically the loudest passenger jet (by far) is the one we haven't seen going over since early this century, won't ever again, and I miss it.
Within next decade we'll probably have small hybrid jets, big ones the decade after, and a decade after that (or maybe earlier after the proven "success" with cars) we'll have people campaigning for the noise to be put back in (maybe you'll be able to request they play "old 747" on approach!). When a small jet can almost (not quite) sneak up on you at 100ft it's scary (seen it with BAe 146 in the 80s), if an electric heavy does it it'll cause heart attacks and road accidents and who knows what.
Heathrow's own website, and Hacan -
HACAN A voice for those under Heathrow flightpaths have a lot of info.
You won't find that exact info though (which may be why google isn't helping) because Heathrow airspace is going to get completely redesigned (
with or without R3) so no one knows yet - search for "flight path changes" on the Hacan page for the timetable and consultation process. With or without R3 it'll probably get better for some, worse for some, and quieter overall (continuing the trend), but the complaints will continue because that is what we do in this country - if it was closed tomorrow plenty of people would complain about that.