2004 explorer front end noise

[Vafordchick]

Hello. I have a 2004 explorer xlt sport. It has new bearings and the ball joints were done recently. For about 6-8 months there has been a noise from the front end. Slight vibration in the wheel. Vibration I can feel in the floor. This prompted me to do bearings twice,ball joints, alignment. It's been in the shop several times. Every time I'm told something different. However the last shop said its the front differential... But they couldn't tell me what was wrong with it. But were happy to give me a repair quote of $4000. (However the front differential is tight.)

Any feedback is appreciated.

Car has 181k on it.