I have a 2011, 4cylinder, Toyota Camry. Each time I start the cold car and begin to drive, I hear a ping or noise while in drive and it stops when I take my foot off the accerator. The noise lasts for 10 or 15 minutes.
Toyota tells me the noise is normal due to engine expansion. "Recommends premium gas but customer will not have to change gas type."
I was also told that retarding the timing will not reduce gas mileage.