Hi Bob,
I had a very bad rattle from the engine bay, that seemed to come from the heating system. At the end, it was the metal pipe wich goes from the intake manifold to the fuel injection pump, between the back of the engine and the firewall. This pipe was touching a metallic point under the firewall, and it made a bad metallic rattle under acceleration, or driving over bumpers.
Another source of rattles could be the front licence plate (when loose bolts), and the two parts of black grille, behind the front chrome grille. If these black grilles have loose bolts (or not all the bolts), they could rattle.
If you have suspension "knocks" driving over bumps, maybe there is some silent block in bad condition. If you jack up the front of the car, you could easily see the condition of the two big rubber silent blocks that fasten the front axle. If you see broken rubber and the inside metalic part of these silent blocks when the front axle goes down, you need to change them (this seems to be quite usual in W113).
Just previous experiences!
Best regards,
Albert de la Torre Chavalera
Barcelona (Catalunya/Spain)
Feb.'64 230 SL Euro Manual