Outer Limits 4x4 Board

A mate with an xj is have a problem with noise when ever he hits the loud pedal, it seems to be coming from the rear suspension. He's has greased the rear shackles and it change for a few minutes, but dose not have the noise when in 4wd or part-time, any ideas it squeks when you push on the rear bar

So when does it make the noise? Is it just when stopped while pushing on the tow bar?

it happens whenever any acceleration put on from a start or on the move when i 2wd but not in awd but can be mimiked by pushing down on the rear bar