I have an 02 mitsu lancer and over the course of 3 days the car has gotten REALLY loud only when accelerating. it sounds like it has been straightpiped but the muffler is still there. Also when accelerating the car vibrates very noticeably - I can feel it in the steering column and the gas pedal. When I have been accelerating and come off the gas, the car makes a loud hiss that sounds like blowoff valves which is weird because this is obviously a naturally aspirated car. I would have thought there could just be a hole in the exhaust system but that doesn’t explain the vibrating and all of these symptoms arose at the same time. What could this be?
Vibrations under load can be many things, but weak or defective engine mounts is a possibility.
Get the exhaust fixed and see if the vibration goes away. Report back.
The loud I assume is like a no muffler noise. Engines require bacpressure from the exhaust system to run properly. Engine missing due to poor backpresure could be a cause. agree with @insightful