I agree with Gove N.T. incoming LHR traffic flies over my workshop east of Heathrow at about 4,000ft, and 380 and 787 are noticeably quieter than other planes. Furthermore their tone is more "centered" with less bassy roar and trebly whine, and the volume seems more consistent. The 380 sounds more like an average twin engine plane, very impressive. When they take of Eastwards they are further south and I cannot form an opinion of their noise.