Have an '08 G35x sedan. Always ran Mobil 1 EP every 7,500 miles with no problems or any oil burning. But the car seemed a bit too loud even though I liked the roar my wife did not, and I read a few posts opining that this oil might be a contributing factor. Pennzoil had offered a $10 rebate on Ultra so I bought a jug and had it changed today at 52,500. Driving home the car seemed noticeably quieter but I assumed it was the suggestion of the posts in the back of my mind. So I picked up my wife, drove and asked if she noticed anything different with the car; she replied it did not seem as loud. Without a decibel reading I can't be sure, but that's my anecdotal evidence.

 

I always think my car sounds smoother and quieter after an oil change, but that's even when I replace it with the same old M1.

 

You're probably right. Sort of like everyone thinking the new brand of tires are superior b/c they changed from 2/32" tread to brand new.