Actually Kremit did touch on something important: pinging/knocking could be caused by (among other things) lean air/fuel (vacuum leak) or increased compression, which could simply be a result of your higher-mileage engine accumulating carbon on the top of the piston. You should consider getting it looked at if the pinging persists or gets worse.
http://www.superchargersonline.com/content.asp?id=104 
