I have an 1988 Volvo 740 that has a brand new exhaust system last year. Recently it has a new sound that can only be heard inside the car. We thought it was the manifold but it is perfectly quiet outside of the car. Does anyone know what this noise could be caused from? We checked the motor mounts and they seem fine. Thank you for any help
*edited to add that this noise sounds just like a manifold has a hole in it* but silent outside the car.