Some times you need to take the service advisor/mechanic/shop manager for a drive so you can show them what you hear! I have ping in mine as well (09) but they could never hear it, hell they could hear the knocking in he bottom and when I spun a bearing before it spun! I went in 5 times before it spun the bearings! I'd hear the noise but they could not!
If its not too bad they will say its fine but you have to keep on them, but when they fix you ping let me know what they changed so I can do mine!
With mine I found it went away with a higher grade of gas, or different gas station.