Today I'm sure I heard a 'tink', 'tink', 'tink' sound coming from my engine. I've never had someone tell me this is what pinging sounds like but I suspect it may be pinging. The sound I heard today could be best described as a hammer very lightly tapping a piece of metal. It was reasonably regular maybe once every 2 seconds. I did have to concentrate and focus on the sound to hear it among the other engine noises (I like listening to the sound of engines).

Reason why I'm posting in this thread is that if my engine was pinging I can't explain why except for the fact that the fuel in my car has been in there for about 18 months (possibly more) and the octane rating has dropped enough to cause the engine to ping. It is 7/8th full. It was filled with regular unleaded at the time.

What do others think?