[thom4782]

My best guess is: worn chain tensioners, worn chain rails, or worn vairocam rails if your car has them. Could be all three. It could also be stretching chains.

Have you checked camshaft deviations and, if so, do you have past numbers to check them against. I believe changing deviations over time suggest wearing rails or stretching chains

You could also check the sump for black or brown plastic pieces to see if the rails are wearing.

Tensioners are cheapest to replace; variocam rails next and internal chain rails are the most expensive requiring a complete tear down.