One way to tell if its binding or rubbing is to gently flick the fan with your finger. Spin it. If its binding it will stop pretty fast. And with no motor noise etc if you listen closely you should be able to hear if one blade is rubbing etc. Turning it slowly with your finger should tell you if its rubbing etc.
I can hear my fan running, if the room is quiet and I listen for it. Just vary gentle buzz.