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Discussion Starter · #1 ·
For minute I thought she was talking to me... after I parked in the garage I heard some sort various noises from under the hood, like a hissing and buzzing, lasted only a couple seconds.

Are battery fans/compressors still going after power down?
 

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The thermal storage system is busy pumping 3 liters of hot coolant, saving it for the next time you start the car.

That retained heat is later used to get the emissions system up to full potential as quickly as possible, allowing the engine to shut off sooner.
 

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John has gotten the first item that happens at nearly every startup or shutdown. But the brake system might also be doing a pressure adjustment or air purge after you power down. A pressure adjustment sounds like a repeated cracking sound. Kind of a very slow buzz. It's pretty loud. If you hear a hissing noise, that is the brake system purging air from the system.

I have heard the break system crack/buzz while coming to a stop and when the car is shut off. I have heard the hissing noise only when I was out of the car and it was powered off. I cannot confirm that the air purge doesn't happen when running. It is too soft of a sound to be heard while running down the road. The crack/buzz does occur during regular driving.
 
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