1996 Jeep Cherokee Front Axle and Differential

Hi, I took my Grand Cherokee into an ice bank last winter, threw off my alignment and didn't think too much of it after that. Had no issues.

So last week I took it in for an alignment, first guy tells me that he cannot do anything due to my front differential being bent. Said it was throwing my suspension off as well and then asked for $2,000 to fix it. Second place I took it to told me that my front driver side u-joint was on it's death bed and the axle was most likely broken with possible differential damage. He took the time to show me that my u-jont had a lot of give in it and it needed to be replaced. Fair enough.

Also as of right now my 4wd is un-usable. I'm getting an almost knocking noise from the front mid to the passenger side of the vehicle. The mechanic at the 2nd place I took it to said that was mostly likely because of the U-joint.

So to get to my question. How am I going to know if there is actual damage to my differential? Is there going to be a tell tale noise that it is going to make? And is the differential the cause of the 4wd issue or the the u-joint like the mechanic said?

Thanks for the help!