OK, not sure if this is related to the previous issue, but check engine light came on again. Autozone pulled codes and this time the error code is "vacuum leak" or something to that effect. Incidentally, the turbo or the engine or something sounds VERY loud at startup, and then quiets down after the car gets hot. Is there some type of vacuum switchover valve that kicks in once temps go up? I'm thinking if there's a vacuum leak, the waste gate might not be sealing properly. Is the waste gate vacuum regulated, or electronic, or both?

Any thoughts?

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