Originally Posted by 1slow370

the only adjustment that can be made would be reshimming the lifters which would cost a hell of a lot and require both heads to be completely torn apart. they could pull your valve covers and check the clearances first with feeler gauges to give you some piece of mind but that would require tearing the top of the motor apart, and i'm not 100% sure whether or not that would require disconnecting the vvel actuator sub assembly which nissan says needs to be replaced if it is ever removed, if they mistakenly take apart the ladder assembly you will be in for new heads as well. your best bet is to keep trying for warranty if you don't like it. It might be a problem with the hydraulic lifters if there is some air trapped in them that can't be bled out and that would again require tearing the heads apart. if it's only coming from the very front of the engine it might be a problem with the chains or tensioners but that is highly unlikely.