I remember staying with friends on holiday at Hartland in North Devon when the bang (anything from no sound at all to the human ear, but all the birds in the district would suddenly give a collective squawk and jump up and down a bit, to a sharp 'crack' like a rifleshot.) This would manifest itself usually a little after 20.00hrs, and shortly afterwards, a contrail would suddenly begin to appear, very high up, and continue until it passed over our heads inbound to Heathrow.
By contrast, all the subsonic traffic could be seen laying contrails right down to the horizon with the sea, and would seemingly take forever to finally overfly us.