I recall being in the Friends of Fighter Collection area at Duxford's Flying Legends once - two guys were running trailer mounted Griffon and Merlin nearby, both beautiful sounding engines yet with those particular short props or the RPM chosen or whatever there was an unpleasant resonance; no idea if we were in the focal point or if it was more widespread. Noticed that the A400 also produces a similar unpleasant noise sometimes when flying overhead outbound Brize, quite painful on the lugs.