G'day W8YE. I think you and I are trying to describe the same sound. I have heard OS open rocker 60s make the same sound that my old Enya 46 4c makes. My Saito 90 3 cylinder radial also made the noise with its standard short muffler stubs. It is not an unpleasant sound, but rather nice. I suspect your "gluke" and my "ploik" are attempts at onomatopoeia (which in turn sounds like a terrible disease but means a word that sounds like what it means as in splash or kerplonk.). Perhaps "gluik" or "pluke".

The sound that a pre-igniting engine makes is less pleasant and more like a tearing cloth or as someone said, frying bacon.