603 intermitent thudding...
 

when i started the car yesterday i noticed a slight thudding sound... it sounded like a heavy piece of cloth that somehow got stuck on the prop shaft and started hitting the undercarriage... the rhythm was quite regular, though not always present... and it went away after a while. Car runs fine, no unusual sounds when running...just when idling.

when i put my hands anywhere on the front of the car a can also feel the thud, its a sharp thud enough to be felt, but it doesn't shake the car.

what could this be? knocking? missing?

i posted a thread about me removing my vac pump because it made a loud clattering sound which disappeared when i applied pressure on the vac pump cover... fearing it could be the culprit i removed it... it was intact, nothing was amiss. will be changing it out anyway since its the original vac pump.

what is the current condition of the belt and and its tensioner?

inspect the way the belt rides on the tensioner

loosen the belt and inspect the tensioner for wiggle or "play"

use a firm stick to place a force on the tensioner while the noise is occurring... if you can do so safely.

X2 jt20,
It may be damage on the belt. Does it make the noise with the car stationary?

its not the tensioner... in fact i just replaced this about a month ago. the belt is fine, frayed at the edges but fine. :) the old tensioner was cocked sideways a bit causing the fraying. everything is aligned regarding the belt.

what does a "miss" sound like with a diesel? how about knocking? IIRC i've never heard an engine knock...

Are you losing any oil?? if so, first thing to check in your head gasket, and you might want to check that anyways..

Injector may be the problem. When the engine is making the noise, loosen the injector lines at the injectors one at a time. If you see that one cylinder is making the noise, move the injector to another cylinder and see if the noise moves.

'Ave a look:
 

@ Flex Discs !

it makes noise stationary... didn't notice it while in transit... and it does it when idling.
i guess that eliminates the flex disk.

Jack up the engine with a wooden block next chance you have.

If the noise goes away, its motor mounts