PacratOld and CrankyPremium,MVM
It sounds metallic to me. I'm guessing it's flashing with an exposed edge or corner. It's also fairly high frequency, which would indicate pretty small in size, so it wont be "obvious" at first glance. I would think that just a dab of roofing adhesive would dampen/kill the vibration. I wouldn't think "nailing" through a new roof would be necessary.
Keep your eye on the ball, your shoulder to the wheel, your nose to the grindstone, and your ear to the ground. Now, try to work in that position!!!