Loud Clunking noise from Front End
So i have a 2003 Rubicon that i bought around a year ago. I do no offroading hardly even though i would like to. Anyways about 3 days ago my front end sounds like from underneath maybe driveshaft is making a clunk,clunk,clunk when accelerating or braking at low speeds. Really cant hear the noise past first gear. Ive tried putting in neutral and has no affect. I took it to a auto mech and he lifted it and i couldnt hear the noise but he said it was my transfer case and should take it to a jeep dealer to look at it. I dont know much about so thinking about taking it in any advice?