The key to the roof light is a stiffener kit that GM put out that minimizes the flexing the light assembly does at hiway speeds. Mine was making a lot of vibration noise until I found out about it. Once I added the stiffeners and replaced the foam gasket that goes around the perimeter of the light assembly all noise and vibration disappeared.
I looked for the P/N of the kit I bought but can't seem to find it. Maybe google it.
Also, the amber lenses pop up on ebay from time to time but you rarely see the entire light assembly.