Don't know the cause of your moan, but the 280 makes a little moan too. Only on cold morning, immediately on moving forward for the first time, and only lasts a second. Haven't figured it outyet, but have a tranny service (filter and fluid) in mind very soon.
'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.