Do inspect the steering coupler.. I get the same noise from my 1980 300sd w116. I just went through an entire front end rebuild, steering tie rods (entire assemblies), upper control arms, lower bushings, new shocks, new lower ball joints, etc., .. there isn't much that I didn't go through.. still had popping noise and sloppy steering...

Had my 6 year old sit in the seat and rock the steering wheel back and forth, I inspected from the top w/ flashlight and saw the 'almost failed' steering coupler. This is a very obvious fix (not so easy DIY so far).

good luck.. and just to restate, IF I WERE YOU, I WOULD NOT BE DRIVING THE CAR AT THIS POINT.. IT COULD GO AT ANY POINT AND YOU'D BE PRAYING FOR A LEFT DRIFT WHILE YOUR CAR GOES OFF THE ROAD TO THE RIGHT....