SwayBar Links
 

I had a clunking in my front end on my 1997 S320.
I read about a guy that's had the same and fixed it with swaybar links and i replace and it fixes them.
Now i have another rattle in the front end, it's not quite the same pitch, but it occurs at the same time.
I bought generic swaybar links, and it's been 3 or so weeks. Is this the problem again?

Best thing to do is get the car up on jack stands and start pushing and pulling suspension and steering parts. Pull the wheels back and forth both horizontally and vertically and listen for noises and feel for movement where there should be no movement.

The W140's are heavy cars and tough on suspension parts.

I don't know what brand you got but I know that Lemforder is the best and are worth the few extra bucks. Three weeks is a bit short for a new link to fail unless it was defective. First try pushing up and down on the front of the car quite fast and see if you can hear the noise this is best done with two people, then get under with both wheels off the ground and have someone move steering wheel back and forth and see if you hear noise. USE JACK STANDS.
Also did you change the sway bar bushings?