I don't have any ghost stories involving a vacuum either but I do HVAC which requires A LOT of time up in attics. Normally there's nothing stored up in there in the newer homes (because of the impracticality that trusses create for usable storage) but in older houses, things are almost always up there and sometimes things get weird. I remember going up into the attic of one really old house which was getting new central heat/air installed for the first time as it originally had steam radiators and a boiler. It was a big old house, and the attic was equally massive. I kept hearing a musical type noise up there. It was intermittent and, as somebody who doesn't believe in ghosts, that may have changed that day. It turned out that yes, there was a really old crank type record player (I think?) against a large gable vent (just a vent, no fan) and the wind would spin the record a little.
I will say that a Bison vacuum looks a little creepy. If I saw one in a dark attic before ever seeing one somewhere else, I'd have to say "what the heck is THAT thing?". The rear of a Royal motor shell kind of looks like a weird alien-esque metallic skull. And you ought to see some of the hugely oversized whole-house fans that some older houses have. They're much, MUCH bigger than the flimsy modern aluminum ones you'd find at Home Depot and look like they'd mangle somebody in an instant. I remember seeing one that was so big that 1) they must have built the house around that fan, 2) I was surprised that it didn't literally blow the roof off from its massive airflow (there was a huge lack of venting in that attic IIRC, just some soffit venting and a small gable vent at each end) and 3) we just left the unit up there and sealed up the cutout where the shutters were since the shroud box for this thing would require the ceiling joists to be cut just to bring it out of the attic -- not worth the risk or cost.