I have a 2001 cherokee, stock with an automatic trans. Whenever the ground is wet or im in soft sand and I give it a little extra gas, the wheels spin. Which isnt a surprise, but when I get back on hard dirt again and the wheels grab, I hear a grinding sound from what I think is the front differential. Almost like a gear isnt meshing together somewhere. It lasts a second or two and its gone. Its doing it in two wheel drive. Any ideas?