in my previous thread i asked about a catalytic converter being bad! well now im starting to think its piston slap! my question is would piston slap just come outta nowhere? cause everything was fine until last friday! i always change my oil at 3,000 miles with either mobil 1 extended performance or royal purple! and either k&n or mobil 1 oil filters! when my engine is warm everything is quiet as normal! however i did notice that when i rev it after it warms up the exhaust makes a popping when i let off the throttle, im thinking its from back pressure but i never noticed it before! im bone stock! and i do have a mechanics stethoscope which put on the cylinder head while it was rattling and everything sounded smooth as can be! WTF is going on! its driving me crazy!