I lived in Fulham for 2 years and on the one or two days that Heathrow was shut down there was a strange unsettling silence. It would usually take a good 15 minutes to realize there wasn't a plane flying overhead every 90 seconds.
How can you live with that amount of noise? isn't it like way too much?
And of course I don't mean you you but in general people living there.
Landings are for all intents and purposes silent. I could sit on the deck and watch airliners landing all day long because they are completely throttled back at that point.
Takeoff, OTOH is a whole other issue. By the time they got over my house in south Minneapolis, they were already turning away (noise abatement procedures I guess), and you got used to it after a while but it was still grating. I learned pretty quick which days to keep the windows closed :-(
What altitude were the planes?
Over Fulham (in London), it's about 3000ft and they're audible as a background rumble. They're so frequent the noise never really stops.
By Richmond at 1800ft it's not possible to have a British-volume conversation outside (Americans might be OK…). By Hounslow (down to ~200ft as they cross the airport boundary) it's uncomfortable.
Heathrow's own numbers say 700,000 Londoners have >55dBA noise from flights. (This is mostly landings, as prevailing winds mean take-off is usually away from London.)
[PDF!] http://www.heathrow.com/file_source/HeathrowNoise/Static/a_q...
It was really bothersome at first but eventually your mind can block it out. Now I live next to a rail track and the train noises don't bother me at all (although they are definitely much less severe).
YMMV though. It probably helped my brain was younger then.
In Richmond, about 1800ft.
In Hounslow, around 1000ft to under 200ft as they cross the perimeter of the airport.
Many of these planes are large jets, 747s and similar. You can usually see the next plane before the first has disappeared from view, and hear both. Between 270,000 and 700,000 people are affected by the noise, depending who you believe.
After renting a house directly under the flight path as a student, I tried never to do so again. Places under the flightpath are slightly cheaper, although anyone new to the area probably doesn't realise the extent of the problem until it's too late.
I didn't think about it for my employer though, and worked for several years directly on the approach path. On some days it wasn't possible to hold a conversation outside. I felt it led to constant stress. On a rare day with no noise (e.g. after the volcanic eruption in Iceland) everyone seemed so happy and relaxed — as if it were the first day of nice weather in spring after a month of rain.
The airport publish this map: http://myneighbourhood.bksv.com/lhr/ which shows that in many areas, there is noise (by some definition) for more than half of the day. (Make sure to tick landing approaches at the bottom.)