It happens on a cold startup when idle goes up .and goes away when idle comes back down. i hear it when i take off from a stop. i had exhuast shop look at it they say they its not converter also i put clamps around it to make sure it wasnt sheild you only hear the noise from right around front doors back on car so definitly not coming from engine area looked at all exhuast sheilds didnt see any loose oh yea only way to make the noise happen when you are parked after its warm is to power brake it