Well. if you look at your transfer case, on the passenger side. There will be either a cable, or a black 3 wire sensor plug at the end just before the output shaft. This is either your speedo cable(going to your speedo which has the vehicle speed sensore), or your vehicle speed sensor. If your speedo stopped working, I would say either he didn't plug it back in all the way, or he didn't screw the cable back to the speedo gear correctly. If you are hearing a whining sound then perhaps that gear is not lined up with the gear on the output shaft.
Or at the worst, they didn't put the little ball that acts as the key for the speedo gear on the output shaft, and the shaft is spinning in the gear.
