I hope its what Malcolm says - mine (yr2000 E240) needed a new rack to shut it up.
Do also try a bit of lube on the rubber supports under the dash.
With the front of the car jacked, you could possibly hear the steering swivels by putting a large bladed screwdriver onto each joint and the handle to your ear, and turning the steering, swivels are a 90% failure as apposed to the steering racks
I can tell which school of engineering you went to Malcolm
lol.. Malcolm you're quite something!
Get some of these from a Vet, the ones they stick in horses, you can fill them with oil and inject through the rubber boot