My cars making funny sounds?

[iamadrummer]

So i'm driving home in my 2003 Honda Civic, I hit about 105 on the highway. As i get to the main road i cruise at 45 mph, I turn down my music and hear. Pshhhhshhhhhshshshshhhhphhppp When i hit the gas it sounds like my car is letting out air with a fart sound.. like a flabby fart sound... What is this? My muffler?? Engine?? Please help me