2002 Ford Mustang GT making a hissing sound when accelerating?

Ok so i don't know much about cars… Ok >.> i know nothing other than the basic stuff a car should know. I have a 2002 Ford Mustang GT and when i cruising it sounds fine but as soon as i push the peddle in just enough to increase speed i get a constant hissing sound from the passengers side of the car, not a friction type hiss but sounds like high pressure air. I guess it sounds like Nitrous from the Need for Speed games if you know what that sounds like, but ofc I'm not using that. Id take it to a mechanic but don't want to waste the cash if its nothing. Any help is appreciated.

If it is a new noise that you did not have before it will not be nothing

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Get it checked at pep boys or something theyll usually check for free but if there's something wrong they will fix it for you right then. OR find someone who knows alot about cars and will look at it for free. BUt get it checked because something may be wrong