I had a horrible noise coming from my sd once... it turns out the crank pulley bolts had ALL let loose. Buy the time I got them replaced only ONE was actually semi holding the pulley on.

Dont forget to get the gasket too...

__________________
08 R320 CDI current

Past
95 E420
87 300D Turbo 5spd
90 300TE
83 300SD
85 300TD
92 400E
85 190D