I have bought a 93YJ with 70,000 miles on the clock. The rear leaf springs are sagging and are shortly to be replaced.
I have found a really strange vibrating noise that is really loud around 40mph. As the speed of the vehicle inreases the tone gets louder.
It sounds similar to a worn wheel bearing, but we have changed them. Although the sound seems to come from the rear axle area its difficult to tell.

When bringing the vehicle to a halt the vibration is really bad like a vehicle with an overly agressive tire stud pattern on tarmac.

Has anybody had similar symptoms?

Can anyone offer a good way of being able to find the problem quickly, rather than spending time and money replacing parts that may not need it?
Sorry if my description is rather poor.