I really believe that this audience noise is a loop. Maybe it came from that actual concert but you can hear the same whistle, whoop, and there's a repetitive "FLEETWOOD!" that recurs about 10 times during the concert footage. For example, during SOTM: "Intense ("FLEETWOOD!") silence as she walked in the room..."

Additionally, this loop appears in the Stevie 1981 concert. I swear to it! You can hear that same "FLEETWOOD!" in there too. I think it's most prevalent in INTK.

Maybe it was supposed to be a subliminal attempt to take over the world...