For the past couple of years at about 1am or 2am in the morning i have occasionally heard the high speed approach of an object which suddenly and rapidly decelerates over the west london area where i live....This is not every week or month although it may well be such.. but the times i have heard it have been always at times stated either 1am or 2 am...A few minutes either side.. last night due to humid weather in uk and me having a bad cough the bedroom windows were open and i was awake at 12.55am when the very distinct noise happened again.. i work for a travel agent and have flown multiple time and once on concord, also living 12 miles from heathrow am well aware of the sound commercial jets make when landing or taking off..In fact they often pass over the house quite low...But this is totally different...If you imagine a high pitch whistle that a fighter jet produces at its top speed it would be similar to that or if one could hear a high velocity bullet? this is far more extreme but the frightening part is it seems to reach this area of london and there is a massive sound of deceleration to an ordinary high speed jet roar but far more intense...The sequence is usually over in about 30/40 secs.. the reason i am contacting you this time is that last night the approach sound was much much faster and the deceleration sound incredibly distinct and rapid and quite disturbing.......I am sorry if i am not explaining this properly but if i could record i would and then you would understand my concern my wish is to be at the window with a clear sky to see what is creating this noise...Ps there is no sonic boom...Just this incredible and sudden rapid change in sound as the incoming screech becomes a deceleration roar..Then just a quickly passes and as i say all in the matter of secs i know of no such plane that could endure such a change in flight mode ..Do you?