roof panel noise

ive got a 97 k1500 ext cab. i have one of those visor things on it that goes on the roof and kinda hangs over the windshield. this morning on the highway on the way to school when i hit about 70mph i noticed a noise, sounds like the roof shakin around or vibrating or something, like if you were to take a piece of sheet metal and shake it a little bit. I am wondering if this has something to do with the visor or what. thanks
-Z