One has to use all senses to narrow down the problem:
Twist your head to help pin point the source.
Look for shiny surface. Scraping is really grinding.
Feel the parts gently and you will be able to feel the vibration. At times touch can even dampen the vibration and it is a dead give away.
Ignore smell and taste
It was interesting to note the change in sound based on direction of rotation. Leading edge of the contact makes more sound than the trailing edge.-> hint shield rubbing the rotor.