If you're mechanical enough to install a transfer case, then this is probably totally obvious--but I had a similar problem. My transfer case was making a howling noise at all times and the mechaninc at the dealership said it would go any day. Also, my TOD lights were flashing around like crazy. The problem was solved by just buying new tires. The TOD system needs all the tires to have pretty close to the exact same diameter, so having ones on the front that are a different brand or are more worn can cause transfer case noises.