Ulix:
That is the sound my engine started with the last time (yep there have been 
TWO occasions of this happening) the flywheel bolts came loose.  One cause of 
this happening, on one of the occasionsl, was that the PREVIOIUS (not me) 
mechanic had put the clutch disk in backwards and its springs rapped against 
the flywheel bolts every time around and loosened them all.
Try a real engine stethoscope and see if you can locate the knocking toward 
the rear of the engine--in the bell housing area.
I too pulled my oil pan, checked everything for looseness, etc.   Is it 
remotely possible that your clutch disk could have been installed backward?
David C.
 
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