Forgive me if this is a stupid question, but I'm pretty new to modding cars and have tried using the search bar but didn't find what I was looking for. A little over a week ago I had a Roush axleback put on. Unfortunately I do not have my own tools at my new place yet so I paid a muffler shop to install it. Before they finished we fired the car up while it was up in the air and checked for any leaks and found none. While driving around I noticed a slight smell with the windows down and thought it was coming from my car. My buddy swore that new mufflers have oil etc on them and that I might smell something at first but it would go away. Anyways here I am a week later and I still smell something. I've gotten under the car and still don't notice any leaks and the smell isn't awful or super noticeable unless I've been driving the car and stop at a light. With the windows up at a light or crusining there is no smell at all. Anyone else have this happen before? Could I be running too lean/rich fuel wise? I have been running 91 octane since the day I got it and am on a stock tune. Don't think that would have anything to do with it, but like I said-I don't know what else it could be?