2002 Honda Civic Engine makes an air fluttering sound

I have an aftermarket turbo on my 02 civic si. My problem doesn't seem to hurt performance but it's definitely a sound that shouldn't be coming from my engine bay. I must add that I just returned from a one year tour in Iraq and my car sat in a garage the majority of that time. My wife drove it a few times to keep things flowing but that's not good enough for a any car, let alone a high performance machine such as mine. ;)
Anways, my question is this: Under moderate acceleration, without kicking in the turbo, there is a fluttering sound emitting from the engine. I can best describe it as air escaping at a rapid pace. In other words, the noise isn't constant, but continous. Could it be a loose spark plug? I checked all my hoses within reach for leaks and I didn't find any. Any suggestions?