’94 Jeep Grand Cherokee rumbling sounds

Whenever I drive my jeep recently, there is severe rumbling that
sounds almost EXACTLY like train wheels when they go over the tracks
and there’s that periodic thud while riding in one. The jeep’s an old
1994, but it’s only got 63,000 miles on it, although the bottom is
entirely rusted out. I think it’s something stuck in the 4 wheel
drive chain(s), or the rusted shocks could be causing it. The
rumbling doesn’t cause the ride to be bumpy, but when reaching higher
speeds, you can clearly feel the vibrations. Also, the rumbling is
alot less while going uphill then vs. downhill, which is why I think
it might be the shocks on the back wheels. what seems to be the
problem?

edit: also, more importantly, is it safe to put off the repairs (cause
I need to get it checked no matter what) for about 6 weeks? It drives
normally in terms of control and doesn’t serve more or anything, but I
need access to the car everyday, including weekends for the next 6
weeks so I can’t afford to put it in the shop for a few days until
then...is this a good idea?

 

Jeeps have notorious rear differential problems. Does the noise come
from the back?

Also the exhaust hanger has a habit off rusting out by the
transmission over the cross member. When this happens it makes all
sorts of noise over all sorts of driving conditions. But this noise is
very apparent right under front seats only. Is this where your noise
is coming from?