When I engage 4wd (electronic) on my 2001 4.6 F150 (20,000 miles) and I lift off the throttle I can hear a whining/roaring noise from the front end. I have not had this truck very long so I don't know if this noise is normal. The noise is gone under acceleration and is not too loud when decerating but I still never forget I'm in 4wd.

Do these trucks all make this type of noise in 4wd?

 

Mine makes slight noises on wet/slippery surfaces. The noise is somewhat as you describe...

It will make nasty noises if I drive on DRY pavement with it on. I don't use 4WD on dry pavement because I want to keep my 4WD capabilites for a while.