Front end noise

I have a loud humming noise in my front end, I took it to my mechanic and he said he thinks its the front differential, but he wouldn't know til he took it apart for 65$. Can someone tell me the symptoms of a diff going out or is already bad. Like I said its a real loud humming noise that's gets louder as I pickup speed. How long can I drive on it? And, what will happen when it goes out completely, and will it mess up the transmission? Thanks.

Have you considered, or ruled out a bad wheel bearing? If it's a wheel bearing, that'd be less of an expense and ordeal than the differential. I've replaced a few myself (on my Blazer tho) so I'm inclined to think that way.

1999 Jeep Cherokee 4x4, 148K. Recent noise started in front end. Sounds like a wheel spinning. No grinding or vibrations. Shifts normal as it always has. Do not notice any issues operating vehicle. Front axle was removed a couple of years ago due to damaged gears. New brake pads 2 months ago. Noise increases as speed increases. Drop into Neutral at 60, noise continues. Checked front drive shaft, not turning. Someone mentioned harmonic balancer, but expect vibration with that and I very little if any at all. Vehicle is probably close to end if this is a major repair. Any ideas what we can check?

I have a 1996 Jeep Grand Cherokee Larado 180,000 miles There is some clunking noise in the front end. I have had the U joints, Cv joint, trans mount and bushing checked The noise starts when the speed gets up to 35 mph and becomes steady around 50 mph This is an automatic with select trac 4 wheel drive I could really use some help figuring out what it is

Check the front hub seals if there dry they will squeek and at higher speeds become a constant.