something similar happened many years ago when my brother inherited his MIL's Buick. [i forget the year, but i'm thinking it was a mid 90's model]
at that time, i was servicing the whole family's rides, plus my own, as i had done for many, many, years.
the oil that had been used for all those years was Wolf's Head 10-40. [my brother's good friend had a franchise for Wolf's Head products]
the Buick was always serviced by the local dealership, which used bulk purchased [unknown brand] 10-30.
anyway, after the first change to the 10-40 Wolf's Head, the Buick's valvetrain developed an unusual noise. i tore that apart and inspected everything except spring pressure, and could find absolutely nothing wrong.
so just for an experiment, i got 5 quarts of 10-30 Wolf's Head oil and changed out the 1-40 that was in it. that oil only had a few hundred miles on it at best, so it was saved for the lawn mower.
and as you have already guessed by now, that engine QUIETED down, and sounded like it always did !
so why did the 10-40 make the valvetrain noisy, and just changing to 10-30 of the same brand make it quiet again ? we have no idea, but in that particular engine, from then on until my brother sold it, 10-30 was what we used, and no noise was heard from it again !
so