High pitch noise with 4wd engaged

So when my truck (1995 3.4) is in 2wd and I am in reverse/drive you can't hear this noise. When I engage 4wd and shift into drive/reverse you can hear a very high pitch noise coming from the rear. You can hear it better on the drivers side, and it will go away if I go back into 2wd. My truck also won't let me shift from 2wd to 4wd well I am in park/reverse/drive. I have to go into neutral to be able to move the shifter, and my 4wd light usually doesn't turn on unless its below freezing and I sit in reverse for 5 minutes. Any ideas?


attached a sound file that you can hear the high pitched noise, and then the dog started barking...