Dash rattles

This subject is old. However, I had a vibrating rattle behind the center speaker on top of the dash. When I removed the center speaker, the rattle continued but if a passenger mashed the dash behind the speaker the rattle stopped. After several attempts with different trys, I finially found a rubber ball about 4 inches in diameter, sqeezed it and pushed it into the speaker hole so that it put pressure on the under side of the dash cover. The speaker is easy to pop out with a dull knife. There is nothing behind the speaker toward the dash the ball will hurt. Be sure you push the ball as far as you can toward the dash upright.
I have several friends with the same condition in the gen 11 Prius so the rattle must be very common but easy to fix.