Unless your differential is a limited slip variety, use 75W90 see:
http://www.redlineoil.com/pdf/5.pdf
I just got two jugs in the UPS for my '87 300D rear end
I doubt the noise will go away though, that usually is a sign of worn bearings. BTDT.

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!