I have a 1999 Grand Cherokee limited with the 4.7l and there is a loud noise and vibration coming from what seems to be the front end. The sound only happens when I am giving the engine gas. The hubs seem tight and the noise is not there while making turns, unless I am accelerating. I have noticed a clunking noise at times when I am backing up and making a turn at the same time. Does anyone have any ideas of the issue? I would hate to just throw parts at it until I find out what the cause was.

 

Check the sway bar links very closely while someone is turning the wheel. They sometimes snap at the top, you may not see it unless turning, and the klunk will be horrendous.
After that I would say U joints on the front shafts, or, check ball joints.