Whaaaaat is this noise?

[YAR1S]

Soooo I thought I heard a rattle in my engine and I lifted the hood and got a friend to rev my engine a little to figure out what was rattling, and to my surprise I heard a lot of air sucking noises....almost like someone had installed a turbo overnight It sounds like a pop off valve when revving from idle , but doesn't make a noise while revving from a rev.....
I had a good look at the hoses visible and felt around and nothing could be felt or seen...... It sounds like its either coming from inside the engine or the part where the air filter box meets the engine.


so, please....
someone explain what this noise could be?
Do I need a new air filter? (havnt changed in 6 months or so..)
Is a vacuum hose loose?


watttttttt?

http://www.youtube.com/watch?v=GLmNPUozXbo