New weird air/liquid leak sound from the engine

[David N.]

Was driving home the long way along an uncompleted freeway, driving mildly spiritedly. I pull into my neighborhood and my CD ends, and I notice a weird sound for the first time. I close my windows (top up), rev the engine a little and realize it's something new, it's coming from the engine compartment, and it's definitely throttle dependent.

It's like a PSSSHHHHT that sustains when the engine is under load. And if I blip it it'll PSHT! sharply, and sometimes again when it returns to idle. It's not the normal little suction sound you get from the outside, because the sound remains when the engine is spinning at 2 or 3k, and mostly because I can hear it from inside the car. I got no CEL, no oil warning, and examining the car afterward I'm not leaking anything. It's not really affecting performance as far as I can tell, although since I've heard the sound I'm in no hurry to really punch it. It sounds like a pipe is spewing something, or an air leak. I'm going to remove the compartment cover tomorrow and check it out before I drive it another foot.

Anyone encountered something like this? Is there a hose or pipe in the intake that commonly springs free or starts to leak?

-David