I wonder if there is a recording of the 18 Shackletons (72 Griffons!) flying over Buckingham Palace on the 6th of June 1952? The Griffon had a harsher sound than the Merlin and I think that I could pick it out in that YouTube clip. Centaurus probably remembers the welcome sound of the Merlin 68s exhausts popping when the throttles were closed for touch down, the 224s didn't do that.