Truck: 2004 STX, 4.6L V8, Manual 4x4 transfer case.

I live in Colorado had have spent a great deal of time in 4x4 at highway speeds over the last couple weeks. Whenever I shift into 4x4, there is a metallic rubbing sound coming from the base of the shift lever. The 4x4 works great, but the high pitched sound is worrisome.

Also, anybody know the safest top speed for driving in 4x4? My old ’97 recommended that you not go over 55. Does that apply for the new trucks as well?

Thanks for the help!