Air cleaner mounts (are they intact?) or motor mounts could easily cause a rattling sound on acceleration. If it's the motor mounts, the rattle could be the fan hitting on the shroud, check out the fan baldes and condition of the shroud.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.