Been a topic that's been up and down for decades on BITOG (early days before the myth was real, my 3VZE DID sound like a tin bucket of bearings after M1 0W40 was installed, and I posted it).
Anyway, noise differences and oils have been described as the placebo effect...to make it appear derived by the poster's imaginations.
Placebo effect, unfortunately isn't an imaginary cure, or a person imagining that they are healed...they actually are (*)
You can google "acoustic emissions engine oil viscosity" and find heaps of stuff...here's a table pulled from a paper. Remember that 3dB is a doubling of the sound pressure, so 6 is pretty decent.
(*) As to the actual placebo effect, Gary Allan use to say that the art of medicine is keeping people entertained until nature takes it's course...I lump placebo effect in there...sometimes people heal themselves.