I could use some help with a problem if anyone has any ideas. When I get to about 30 or 40 mph my jeep starts making alot of noise. It's sounds like grinding metal, clanking and some bad vibrations too. It stops when I put it in 4x4. I'm thinking it must be the t-case, but I'm not sure. The jeep is an 86' with 270,000+ miles. It has the np207 t-case. It is a 5 speed. If any other info would be helpful just let me know.