Engine is really loud right now whenever it is running?

I have a 2001 Chevy s-10. One morning at college, i was starting up my truck and it just started to make a really loud sound. Something like what happens when you take the muffler off. However, the noise is not coming from the back, it is somewhere under the hood. The truck is really loud right now whenever it is running. It seems like I have to press extra hard on the gas pedal when going up hill but i may be imagining that part. A friend says that it sounds like there is a hole in a pipe somewhere. I don't know if the donut needs replaced or if there is a problem with the the Exhaust.