The Intriguing Case of a Door Knocking

An engineering student at Sheffield Uni has a theory on the 6-11 case. Cusick suggests Hem Holt's resonance - infra sound on steroids. Long tubes like corridors and lift shafts can build up standing waves inside them as pressure waves travel up to one end, bounce back and interfere with themselves coming the other way. All it would take is a gust of wind,. roughly the right strength and direction, to trigger a resonance. The moment that the door is opened, the pressure across it equalises and it stops rattling... leaving seemingly nothing on the other side causing the force.