When your exhaust manifold gasket is bad your engine will usually sound louder especially on one side where the exhaust manifold gasket is leaking.
Some cars have only once exhaust manifold while other cars engines have 2 exhaust manifolds.
If your cars engine has been running quieter before then suddenly starts running louder while running then the exhaust manifold gasket can be bad especially if your muffler is in good shape.
An exhaust manifold gasket leak can also cause a decrease in engine performance and an increase in fuel consumption.
You could lift the hood and place a piece of paper near the exhaust manifold and see if it's blowing the paper around and if so then the exhaust manifold gasket is likely bad.
Also smelling exhaust around the exhaust manifold is another way to know if the exhaust manifold gasket is bad.
You can drive with an exhaust manifold gasket leak and I did on an old beater car that was not worth repairing and the exhaust manifold was way in the back underneath a bunch of other stuff and it was not worth it to replace it.
I just drove the car like it until I got rid of the car.
But if you can replace the exhaust manifold gasket then I would advise you do so.