I have not hit anything etc. Suddenly my usually quiet corolla has this lingering vibration noise emenatinng from under or in the driver's side dash. It sort of sounds like if you have an empty can of soda, lift the tab and fling or flick the tab...sort of a tin sounding vibration. It occurs when I hit certain patches of rough road. At first I though it was the spring attached to the brake but thas not it. Its driving me crazy. Any ideas?