ptaylor: What I believe that you are hearing is the secondary air pump turning on. The reason you are hearing a "vacuum" sound and why the check engine light is because you either a. have a near-death sec. vac. pump b. have a leaking hose/connection or c.other leaking vac. hoses. It is normal to hear the sound a little, but from what you have described it sounds as if there is most likely a leak and this also contributing to the check engine light.
There is one other possiblility but I don't feel is near as likely because of the ability to "turn itself off". And that is the crankcase vent valve. When these things go bad on the 4 cyl. they usually make a real loud vac. sound and will also cause unresponsiveness with the engine.
So, you either need to attempt to examine the car yourself or take it to a qualified reputable repair facility and have the faults read.
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