CMFarrar

I have a 99 jeep cherokee classic. I am pretty sure the t-case is a 231 (Part-time 4 Hi, Neutral, 4 Lo in that order). When I engage the 4 Hi or Lo there is an ungodly grinding noise that comes from either the t case of the front axle. If I press the gas the grinding gets worse, then i press the break and its slows to a stop. I took the jeep to a mechanic and he lifted the jeep on the riser and engaged the 4 Hi. While the jeep was in the air the front and rear tires spun once the 4 Hi was engaged, but when the jeep was lowered, as soon as the tires met resistance with the ground the grinding began. the mechanic said i needed a new t case, but I want another opinion. If you have any idea what could be wrong please let me know. winter is coming soon and its snows a ton here.