TB - perhaps 'unusual' would be a better description of what you saw? In certain atmospheric conditions shock waves ARE visible to the naked eye - normally 'Schlieren' photography is required in a wind tunnel to visualise them. I'm not sure whether it is humidity or what that determines their appearance, but I have seen probably 5 occasions in my 'passengering' times, the MOST remarkable being a real
'lambda foot' shock on a wing. (Left-hand pic shows it best). That I think is a rare thing to see. There is that famous picture (on Pprune somewhere, no doubt!) of a just subsonic fly-by by an ?F-14? of a US carrier, where the shock forming on the canopy can clearly be seen.
" They're coming to take me away, ha-ha!"