I happened to have seen the first message or 2 regarding 747 approaches into LHR in another forum. However, you cannot assume that all those who post here also read all the posts in all the conferences.
If the ADPs are considered a significant source of noise on one of the quietest airplanes around, and someone is suggesting they be turned off on approach -- one of the most critical phases of flight -- then those people need to re-examine what has gone into attaining the level of aircraft safety we have now!
A couple years ago our airline found a very high correlation between the rate of tire failures on our 747-200 fleet and the use of flaps 25 for landing. Our -400 fleet has always used flaps 30. To prevent a tire failure and its possible consequences, ANYONE should accept another decibel of noise in this context.