Stopped at a gas station while traveling. When I restarted engine heard a bubbling or pump rattling like sound coming from under the drivers side floor. Checked all fluids and they were fine. No gauges changed. Once I got home and restarted it sounded more like an exhaust noise. Don't hear it from above the engine area - more inside the car and underneath the drivers side. I had the exhaust manifold replaced last October 2012 could it be a sensor?