I think you are right. There has definitely been a change in the Heathrow flight pattern over-head. I have only just started to make an effort to try to monitor it but perhaps the aircraft are now flying lower over south east London or there are just many more of them but it seems impossible to find a time during the *entire* day when either the whine of a small aircraft or the drone of a large one is not oppressively, or annoyingly audible! Just as one is on the brink of out of range, another comes in. I am sure this was not the case say 3 months ago. I have frequently been disturbed by an aircraft overhead around 4:30am, then another around 5am, then 20minute to 10minute intervals for the rest of the early morning and then flights overhead at around 3 minute intervals during the rest of the day (I can only vouch for the weekends on that) till late at night.