I have a 3723A, which is in the same product line, so I'd expect it to have a similar internal build as the 3721A. The fans are noisy, and they also have the same "rubbing" or buzzing sound as in your video. It's hard to tell, but yours might be a little louder.
I would take the cover off and check for anything obvious in the way of the blades. There are two fans, at least in the 3723A, so try disconnecting one at a time to see if one of them is the culprit.
Test equipment manufacturers aren't generally looking for the quietest fans when spec'ing their parts. You could always replace them with quieter fans with the same rating if it continues to bother you. It might be a little work getting them out, though, since they're inside the metal air duct around the heat sinks.
Or, since it's new, you could ask for a swap for a different unit.
(Edit: Fix ambiguity.)