I just bought a 2002 Sentra Se-R after driving Hondas for years When my Si finally gave up the ghost (Oil consumption problem along with many other problems) i decided to go with a Nissan. When the engine temp gets up to normal operating tempeture, there is a pinging noise all the time (i only hear it when im idling at a stoplight or when i pull in the garage) it also continues to do it after i shut the car off, it stops after the engine cools down. Im assuming this has something to do with the exhaust getting normally hot but i just want to make sure this is normal. All my car friends say its normal, it is basically just the "cooling down" noise after you shut off the engine. Its just a constant ticking noise only after the engine gets warm. Could this have something to do with too low of an octane fuel and this is the dreaded "knocking", (i usually use 87 octane)? Im not used to Nissan Q engines so im not real sure of their operating procedures, I know this might be a beginner question, but i just want to make sure while it is still in the warranty. Thanks, any info would be appreciated.