i have had 3 max. 2 sitting in the shop and one my friend drives.so total 6 max. 3 makes a slight rattling, growl, almost like and exhaust leak at idle. but when revving the motor, i can hear the growling or rattling noise right by the iacv or around that area. i can not seem to find out what is causing it. i thought it was a loose y pipe gasket first, then iacv, then the egr tube. i checked and tighten the y pipe no leaks, changed in a new iacv or newer throttle body, and cleaned egr tube and tighten it as well. still got same problem. the noise was not that noticable before but is worse now. i also notice a good bit of my low end power is gone. i doesn't pull as hard. i even changed the 6 new coils, new plugs, fluids, and filter. pcv as well. still same problem. it seems better for the first couple of days then right back to where lagging again. can someone tell me if i have a common problem? or what they did? i mean all 6 max make the noise but only 3 is noticable. mine is the loudest. i would appreicaite the help.