I have a 4cyl. 2011 slt... I have a pinging noise coming from the exhaust pipe.. notice it when sitting at a light or idle.. at first I though an acorn hit my car, it sounds the same, but then I noticed its coming from under the car area... I have 3000 miles on my truck, I know there is some noise from a new vehicle, metal exhaust pipe getting hot and cold etc... but this is very annoying and it doesnt seem to be going away.. anyone else have this issue?