While we are on the subject of fans. When I bought my 1923 it had a funny noise that took me a while to track down. The issue was the 5 rivets that fasten the blade spider to the hub were worn and loose. Really loose. I ended up removing all 5 rivets, slightly over size drilling the 5 spider and hub holes and installing 1/4-28 grade 5 bolts and center punching the nuts in several places to keep them from moving. That was 28 years ago.
Grab those fan blades and see what the hub and blade rivets are doing.