Understand completely that the 4.7 litre Chrysler and the GM5.3 have nothing in common. I just cited that I had the same thing happen that he is experiencing at about the same mileage.
Did you switch from one synthetic to another though? He did, he went from a Mobil 1 product to a LiquiMoly one with about the biggest difference I can see being that one was a high mileage oil, which are typically a touch heavier for the grade and have added seal conditions and the like, to one that wasn't.
Well they all are made from base stocks, I think you accidentally missed a few words in there In the case of the oils the OP is running, both are likely majority Group III, so base stock selection between the two is probably quite similar. And of course the GTL base stocks used by Shell are also technically Group III, like Mobil's VISOM product, even though the process is different.Most synthetics are made from base stocks or natural gas derivatives,
but like I said, others have reported noisier engines when they switch to or run total synthetics vs syn blends, or straight dino oil, especially in older worn or low clearance engines. I too have heard good things about the Castrol Magnatec, but I have never used it myself. I will have to try it out at next OCI.
The moral I guess is, find out what works for you; oil brand, derivative, viscosity, filter, additives. Whatever combination makes the noise disappear, document that, and then keep on using it.
Personally, I'd try and confirm it isn't just an exhaust leak first, and once that's verified, perhaps switch back to the oil he was using previously. Seems the most straight-forward in this case as either the noise is related to the oil brand change or it isn't.