Vintage Cars: Mercedes 300E deceleration noise, banjo bolt, rear differential

Question
My 88 300E makes this chirping / squanching noise when decelerating.  It's coming from the left rear of the car.  But, I get no noise (at all) from spinning the left rear wheel when it's off the ground.  Any ideas?

Answer
my first thought is flex disc , either front or rear or both.  MB do not use universal joints, but rubberflex discs.  You will see them.  If they are bad they could have play or the rubber is cracked, bolts may be gone. DO NOT IGNORE IF THEY LOOK BAD OR HAVE PLAY. When they fail at speed the result is catastrophic.  A whine or squeal is usually a warning sign.  If they check out then  I would make sure the rear differential is full and the air gap is unplugged ( It is the banjo bolt on top of the rear diff that allows it to breath)
Let me know what you find
Ron