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I assume its the AC... when I turn the car off after driving home (30 miles) I hear a high pitched constant squeal coming from under the hood. I stood there today waiting for it to stop and it took about 3-5 mins. I also noticed a loud bang almost noise from under the hood after i turned the car off and was sitting inside playing with the setup options under Accessory power mode.

Are these things normal?
 

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It might be a cooling fan which is staying on for a short period after you park.

Loud bangs are definitely abnormal :eek:
Yeah, I tend to agree, a bang from the CT = bad!
 

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I noticed the same thing after I parked the car in the garage. I hadn't made any assumptions about what it was, but the a/c is a good guess. I assume it has something to do with something overheating since it happened in 100+ degree heat. Sometimes fans will stay on after you turn a car off to keep cooling things down, but they don't typically make such a high-pitched noise.

Did you get any answers from the service center about what it was?
 

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Bangs are definitely bad. If there's a high pitched whirring noise, it could be the water pump finishing up a round of recirculation.

Our cars actually have a split radiator. One part of the radiator provides coolant to the engine. The other part of the radiator provides coolant to our inverter. Our inverters actually have little channels that run alongside the electronics in the inverter to help cool it down rapidly. The inverter gets REALLY REALLY hot during operation as it converts DC to AC and vice versa and does some other fun things to get the car going. That might be what the noise is.

I don't usually hear bangs, but I do hear some loud clicks every once in a while after powering down. I also hear some clicking when I enter my car before starting it and after unlocking it. I think that's the pump circulating some coolant in preparation for starting the car.
 

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I get the same whining high pitch noise when I park the car after a hot day with AC running. I looked under the hood and it is coming from the AC system. I assume it is the compressed gas returning to the main chamber after the compressor turns off. Nothing to worry about at all. However, the bang is an issue that needs to be addressed.
 

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The CT200 is built on the Prius platform. I assume the sound you are hearing is the coolant being moved to a tank that helps maintain its temperature between driving sessions. It is intended to reduce fuel consumption by reducing the time needed for the system to reach normal operating temperature. Obviously, a much bigger deal in the winter.
 

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I thought this was a neat picture

 
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