I'm experiencing a problem with the front differential on a '06 F-150. When it is in 2 wheel high, the left front side is making a noise like some tin is rattling and lightly scraping. Not grinding though. When the vehicle is in 4 wheel high, the noise stops. Does anyone know what this might be? It's only on the left front side.

 

I realize the date on this thread, but I was just browsing through some threads that dead ended more or less. I can comfortably say the problem with this truck is in the Vacuum actuated hubs. Thought I'd throw my 2 cents in just in case someone else experienced the same issue and was looking for a solution.