1982 240 D rear noise
 

I have a manual transmission 1982 D, makes a bumpingnoise in rear, not all of the time, was told by one mechanic it was the axle, another it was not...any suggestions, Also what is the cutoff limit to invest in this car, I bought it for 500 body/ interior in excellent condition, engine runs good, had to put new tires and shocks on it but until this noise that was it.
Help me if you can.