Firstly, apologies if this isn't the best forum to ask the question. I mentioned on another thread that the BBMF's Spitfire
PR XIX landed at Cosford yesterday on a weather diversion and made a lot of people very happy in the process. After the aircraft had taxyed past us and departed with the usual glorious audio accompaniment, several of us were subsequently wondering why the Griffon sounds almost as though it's only running on one bank of cylinders when running at low RPM. In fact at one stage it sounded for all the world like a rotary engine being 'blipped'.
I don't recall Shackletons sounding like that but another spectator observed that the Sea Fury's Centaurus sounds very similar ("like a bag of bolts" was the expression used) at low power. Is this a general characteristic of big piston engines, and if so why?