Yelp

I recently bought a 99 wj AWD with low miles and I went out of town to see family and I had to drive down a dirt road that had a bunch of clay and it previously rained and while I was on the dirt road I had to give it a little gas and when I did I felt all tiers start to spin and as soon as they did this god awful crunching noise started. It sounded like it was right under my center console. It dose it every time all the tiers spin. Could anyone know what is happing.