To be clear, I have (almost) no experience on the type.
But an episode at Haneda 26 years ago is very vivid in my memory. I was to ride jump seat in a newly-delivered All Nippon 747SR, and was lounging in the upper deck waiting for a gaggle of NH techs to complete their cockpit orientation tour.
I heard a foghorn-like sound begin, which I thought was some hydraulic noise. I tried to deduce what the trainees were doing to make such a sound - until I happened to glance outside. 500m down the ramp a 1011 was emitting a fog from #2 - just like the Roswell video. It took at least 2 min. for the fog generator to cease, at which time the foghorn also stopped.