The car has been running fine lately. When I pulled up to put the car in park I noticed a low grumbling noise underneath the car. Sounds like an exhaust rumble so I left it running and went to the exhaust but the noise was coming from underneath the car under where the passenger seat is. Any ideas? Thanks guys

~jon

 

Possible exhaust flange joint blowing the donut seal, check the 3 bolts at the flange joint.
Check O2 sensor is still there and not loose. Pipe hangers etc.