I have a 2001 Buick Century that started making a noise from what seems to be the engine. It sounds like a jet engine when I accelerate. The noise is still there when I cruise, but it evens out. It is loudest when going between 40 and 50mph. The car is not overheating, and other then the noise it drives fine. My husband at first thought it sounded like the catalytic converter had been stolen, but he rarely knows what he is talking about. What could it be, and how much would it cost to fix?
By “jet engine” do you mean loud or do you mean a high-pitched whine? Get it checked right away, because if the exhaust system is broken, you can get CO in the car. That’s Carbon Monoxide not Colorado. 
The noise needs to be isolated first to know what kind of problem you have. so is the noise there when sitting still or is it only while vehicle is in motion ?