[MBZ] 1979 240D, Noise in back end

[ts]

Car is a 1979 240D, 123 chassis, daily driver with 102,000 original miles. I 
notice when I take my foot off the accelerator a low rumbling noise in the 
back end when I am coasting down a hill for example. No noise when the 
accelerator is on or cruise on. Just had the rear links replaced on rear 
tor. sway bar. Fluids are synthetic in the rear diffy and are full. Any 
thoughts on what could cause this? car runs exceptionally well with highway 
mileage in the high 20s low 30s mpg. Car shifts fine and tranny is fine. 
Just adjusted valves ect. Not a wheel bearing I do not believe or could it 
be??

Only makes the noise when you go to coast and it is a low rumbling noise, 
not excessively loud

Jus wondering what project I face, thanks Tom