I found this issue with even petrol quality if you dont know the filling station well. Same goes for oil change shops, I hardly trust an oil shop with quality, always buy your own oil from trusted source and get it changed.
Your trip reminded of one of mine with friends back in the college days from Lahore to KPK, and my perfectly tuned corolla 86 started knocking soon after fuel tank filled from lahore was finished. Un aware of the issue, all along with trip, we changed oil, plugs, filters etc but no avail so we assumed it may just be we all four and ac is taking its toll....... but on the way back as soon as we hit the good fuel station by chance on GT road, ( and that was station in the middle of two bridges at River Chenab) car roared back to its normal power!
We should use Google map and write reviews of oil, mechanic, filling stations so we can check before using them!