I think this depends a lot on the rider and their level of experience (just like it does with drivers). Modern ICE cars are so quiet (to the point that many cabins feature ANC to help mask engine noise) that you'd never be able to hear a whining belt or misfiring spark plugs, and perhaps not even squeaking brake pads. Bikes are similar but the rider is much more directly connected; even so, many riders are pretty oblivious to how they work or how to fix problems.