We have a 2014 terrain (91,000 miles) and we're smelling exhaust fumes inside the cabin (especially while idling, like waiting in a drive-thru). The car is not super 'loud', but it has gotten a little louder over the last few months. Seems to quiet down just a tad after start-up. I have seen several mention it could be the manifold. The service engine light is NOT on. Just wondering if it might be something else or if it definitely sounds like a bad manifold.