By the sounds of your problem it seems to be a bad vacumn causing the Tcase to not fully lock in 4x4.if the Encoder motor on the Tcase and the TCCM are making noises then the motors themselves are getting voltage so try looking at the vacumn line under the battery tray under the battery. If there are any cracks or tears in the line or even dirt/debris it will cause the vacumn line to not seat fully and not lock the encoder motor in. Its best if you have 2 people 1 person inside switching the 4x4 mode and another looking at the vacumn line itself to make sure its moving and to see if it seets fully. The motor itself is about $30 if thats the faulty part and it is fairly common, had to replace my buddys on his ZR2.