Diff troubles...??

I think I may have a problem..I have a 2011 jeep jk sport with a pr44 front and the factory Dana 44 in the rear. In each axle I have a Detroit locker and 37" tires.. Unfortunately I am living in the city and the jeep has sat for about 2 months where it has been stored because I cannot have it here. I started it up the other day for a drive and it didn't want to move. It's standard and I thought it could be the clutch but when I finally got it to move I heard a loud "clunk" sort of sound which leads me to believe it's the diff..?? Could this be the Detroit and the lack of fluid movement in the diff for so long..?? Any help is appreciated.

Also I might add that I got it to move because I had to use 4low, and that is when I heard the sound. Thanks gain for any help

I wouldn't think two months is enough to ruin the diff fluid or the Detroit. Did you pull the diff covers to check the fluid?

My guess would be a brake lining stuck. Very common with drum brakes, if you have rear disc, it could gave been a park brake stuck.

Yes I did pull the cover and change the fluid and it looked ok (no pieces of metal or broken visible components).. I will be back this weekend and I'll see if the same thing happens. Thanks for the help.