Transfer Case problems of the 2003 Jeep Grand Cherokee

2003 Jeep Grand Cherokee I purchased from neuwirth car dealership, in wilmington, nc. The reason I now own this vehicle is because the first Jeep they sold me feel under the nc lemon law and the information was not disclosed to me before I purchased the first Jeep and I returned it 3 times for the same problem the driveshaft. The problem with this one is you can not put it in 4 wheel drive unless you use both hands and push hard on the floor to shift the gear, they said they would replace the transfer case, but when they called another dealer they had replaced the case in 2 others and said the noise was still there, that it would not make a difference if they replaced it. So far they have not replaced it. It makes a humming noise while sitting idle at a stop light, and made a loud clinging sound when I put it in reverse, (took it back twice before they fixed it) they said it was normal for the clinging sound the second time I took it in it cost them 1300 to fix "nothing". I still have the humming it's worse now, and the clinging noise comes and goes. They do not know why. When I called mr. Gillilan at the dealership, he said what do you want me to do about it" he said the only choices I had was to trade again but it would cost me money, or let them keep trying until the problem is fixed, how can they fix the problem if they don't know what the problem is and how long will this take. I have missed work hours and days dealing with these Chrysler vehicles. I would tell you what the problem is but they don't know to tell me. I can't have it looked at by any one else because it would void my warranty. It's not that I don't like the car but I think if I'm paying all of this money for this vehicle I should be happy, by at this time I'm very unhappy with the performance and the answers I'm receiving from this dealer. I have owned this vehicle for 3 months thank you for your time.