My MPV has recently started making a really loud noise - similar to an outboard motor or motorcycle - whenever the car is running. It’s on all the time but gets louder when I step on the accelerator. Car has 65K miles and has been a money pit of late. If it’s a relatively inexpensive problem we’ll get it fixed, otherwise trading it in.
You need someone to inspect the exhaust system. Something has let loose, but it would be impossible to say what - anything from the manifold to the muffler. The manifold would probably turn out to be the most expensive thing. A new muffler or section of pipe would be not such a big deal.