Can someone help me!

i just brought a 98 mountaineer awd....I hear a grinding noise when I'm driving, I have been told that it is either the transfer case or the t/case motor...They say the car is switching between low and hi gear does this sound right? they say they can drain the fluid then they can tell which one it is my question is .... could it be anything else like the engine?:screwy:

The reason for draining the oil is to check it for abnormal particles, i.e. metal grit. Also, seems to me that I remember that some Mountaineers have a problem with a grinding sound that is damn near impossible to find? The '98 that I use to own would occasionally make that sound, but I could never figure out what was causing it. The problem correct itself when an idiot ran into my stopped Mountaineer and totalled it out! I now have a 2000 Mountaineer but without that weard noise.