Weird Noise

What is your question?

I have an 06 Maxima SL. When I purchased the car, it was running fine and still is. I just noticed a weird noise. It's coming from the passenger side under the hood. Don't know how to describe it other than it sounds like a flutter - I really thought a bird had gotten caught under my car somehow. It only makes this noise when I accelerate. If I'm in park or just sitting, doesn't make a sound.