I have identified an issue with 2015 corolla manifold gasket which after sometime causes noise under the hood while driving as well when the engine is off as the car moves while stepping out of the car while the engine and exhaust system is warm. This noise increases over the period of time as the gasket is rubbing with flex pipe and eventually will create a leak in the exhaust system and possibly damage other engine components. Leak would produce hazardous gases and could hurt passengers if gets into the cabin. This is the problem with all corollas and do not know how far it goes back. As Toyota do not have any solution for this issue as this is a serious design flaw and possible part issue, they are calling it a normal characteristic in public although it has been acknowledged an issue in private by a Toyota Engineer. This part has been replaced couple of times in my car after visiting 6 times under warranty and initially there will be no noise but then noise comes back as you drive more. You may not hear the noise under the hood while driving due to closed door as well engine noise. This is just not a noise issue but an issue in the power train system and will bite you in a long run if you plan to keep the car for long. Toyota tried to settle with me by giving some extended warranty but asked me to sign a release form. If this is not a serious issue or could become a serious down the road they would have not asked me to sign a release form. Toyota has no plan to fix this issue as this is a design flaw and they do not want to make most of the customers know. Buyer Beware. Please visit your dealer and hear the noise under the hood near the manifold gasket when you step out of the car as the car moves or push the car just to hear the noise while the engine and exhaust system is warm. This is not just a noise issue that some people may ignore initially but could cause serious issues and financial implications over the period of time. This may be a slow damage of power train components and may not be easy to prove. I have tested 2014 vehicle also and was able to reproduce the noise. Toyota as always will not do anything unless it becomes serious issue or becomes a media story.