So my 1999 3.9 dodge V6 with 155,000 has seen castrol/valvoline dino all its life. The last oil change I ran Penn yellow bottle with auto rx, I decided to put Penn Platinum in it for the rinse. On yellow bottle it purred like a kitten, its first dose of synthetic its sounds awful. Let me say it sounds awful at idle, just not the quiet smoothness I had with dino. Weird. I reckon back to yellow bottle. My ears don't deceive me. Any thoughts?