Having a problem with my 4 wheel drive, its not working and hasnt for about a year, I heard a loud pop while backing the boat in the driveway (foot of snow) and that was all she wrote. Its a manual shift on the floor, I still get the indicator lights in 4x4 high and low. Today we jacked up the front end, and you could tell it was engaging when we manually applied vaccum to the lines. But its almost like something is stripped or something? Hear alot of rattling underneath the truck and the front wheels arent engaging when i took it out in the yard. Any ideas on where to start, or what to check first? We tested the selonoid and it seemed to be fine. The rattling didnt seem to be coming from around the wheels, more like the middle of the undercarriage. I am assuming its something trashed inside the transfer case?? I know my way around a motor, but once ya get into transmissions and transfer cases etc, I am lost. Thanks in advance for any help..