My 300tdi has that clatter. I spent ages trying to figure out what it was, no success.
Then I had to replace the head gasket. Took the head to be resurfaced, and was told that someone had already taken a cut and no more could be machined off, but the head was flat anyway.
They estimated about 0.5mm had been machined off.
Checked the valve head stand down, and they were all close to the limit due to the head machining.
Put it all back together and all good re gasket seal, but the clatter was still there.
Happened to do a compression check and found that 3 cylinders were at spec., but no.2 was noticeably higher than the rest, about 30psi higher.
So I reckon the clatter is coming from no. 2 cylinder, compression is too high.
Hope the big end bearing survives.
Terry
80 109" 2.6 P ex Army GS, saved from the scrappie.
95 300tdi 130 Single cab tray.
2010 Guzzi 750
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