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.
There's a similar arrangement at Gatwick. When they arrive from one particular direction, they fly low over the long-term car parks, which sets off all the alarms - repeatedly, until the batteries go flat. You come back from a week in the sun and the car doesn't start! Fortunately, they are used to this and have a huge battery on a trolley with jump leads, so panic not! Just thought I'd let you know....