I have an "81 SD. It had a definite metallic knock. I cracked the injector lines one by one ,at the injectors, untill the noise went away. There is an extensive thread titled "knockin "81 300SD". Which chronicals my travails. But the main point being I was able to isolate the noise to one cylinder. It just so happened that it was no.1 cylinder on mine. Hope this helps. Lee

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'83 300D 283,000 mi.
'88 Jaguar XJ40 132,000 mi.(sold)
'88 Olds 88 190,000 mi.(given to grandson)
'81 300SD 313,000 mi. (given to granddaughter)
Maintained by Me and my offspring.
ESCHEW OBFUSCATION