I have about 6-7k mi on the odometer since last oil change. I only use the motorcraft FL-500S filter, and prior to last oil change I was getting free changes at the dealer using motorcraft oil, and last change I used Pennzoil Platinum 5W-30 Full Synthetic Motor Oil. I plan on using that oil again this time when I change it.
I just filled the tank with some shell 93, about 14.x gallons. I went to the gym this AM, on the way home got gas, and when I parked in my carport, I revved the engine in the same manner and I didn't hear that sound anymore.... Maybe my gas was a little questionable in the tank before?