I did quite a lot of research into flights into Heathrow a couple of years ago. Heathrow never closes but the number of flights they are allowed during the night (basically 11pm to 6am if I remember rightly) is very limited. In practice they seem to use most of ther night time allowance beteween obout 0430 and 0530. This is most noticeable during the summer when people have their windows open. It is also only noticeable round here if they are landing to the west - which they do the majority of the time although the strange weather patterns recently have meant quite a lot of quiet days as they approach to the east.

City arrivals are only noticeable here it they are landing to the east - which I'd guess they only do around 30% (or less) of the time. When I really notice the planes is when Heathrow is landing to the west and City to the east. This happens when there is a light easterly wind. Heathrow flights can accept a small downwind component for landing and taking off because the runways are long. It is done to minimise the noise of departing aircraft over London. With its relatively short runway, City arrivals will almost always land into the wind to minimise their ground speed on landing (and maximise their airspeed on takeoff).

If you want to see the actual heights of every plane arriving at Heathrow you can check it a day or so in arrears at http://lhr.webtrak-lochard.com/template/index.html. I don't think you will find that they ever come over us at less than 3000'.

City arrivals are lower, but they tend to pass over very quickly and are smaller, quieter planes which most people seem to find not a problem.

Compared with the continuous traffic noise that many people living in London have to accept, aeroplane noise seems to be a low level concern except, obviously, for those people who have, for the most part chosen to live close to one of the world's busiest airports.

Fortunately modern planes are a lot quieter than earlier jets (like the 707) and they are getting quieter still. And we don't get our early morning wake up call from Concorde any more!

Hope this helps.