I've never had a rattler actually rattle at me and I've had a LOT of encounters when I lived and hunted in Arizona. Been face to face with a rattler while down on my hands and knees looking for dove and quail I shoot in the under brush, came within 6 inches of stepping down on a coiled one, climbing cliffs and they are on the shelf etc.
I have heard a large Western diamondback rattler going off and they are amazingly loud.