I have been having pinging sounds coming from the engine at around 4-5 rpms...especially when cold. I have tried everything including fuel/engine cleaners, new plugs, dealer visits, etc.
Last week I took car in for oil change and also had all my gear/tranny oils changed (30K mi).
PINGING COMPLETELY GONE. I dont know why.
I have been told that it was coming from intake "flutter" to dirty carbon build up, and many others. Changing tranny oils seemed to cure the problem :)