I don't think it's oil retaining valves as they would only cause knocking on cold starts when oil has drained to sump and would not affect warm running when the oil pressure builds up.
It does sound like like possibly low oil pressure when the oil heats up and becomes thinner. Is it mechanical knocking or just different combustion noise more like old diesel. Our A6 would sometimes got funny combustion noise when EGR valve was dodgy it sounded more like older diesels.
I guess there was no knocking before change of parts.
Sorry I cannot help much but I will definitely follow this thread as I guess our A6 will need the same job doing sooner or later as it's almost 200k miles now. I guess you have older style engine without rollers on rocker arms same as our A6. If you have any tips and if you could let us know what parts you used and where did you get them from that would be great.
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Currently 8less
2011 Q7 S Line 3.0TDI, 2016 Tesla Model S 90D
8 history:
2006 A8 Sport 4.2TDI quattro SOLD,
1997 S8, reached end of life with gearbox failure
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