High pitched whistle under the hood

It's odd because it always makes that sound to some degree, but more so when it's between 0 & 8 degrees C. I have had it into the dealership 3 times complaining about it, and they say that they didn't hear anything weird/it's normal. I have only had time to drop it off before work and leave it, but I think I might bring it in, and ask to test drive one on the lot, because I certainly don't remember hearing that noise when I test drove one before buying.

When you go in when it's making the noise, get them to sit with you whilst driving
 
When I turn off the car, there is a High pitched whistle coming from under the hood. Lasts about 30 seconds or so. Is this normal? Could it be the flux capacitor? (eyeballs)

must be Yondu from Guardians of Galaxy, might be broken you must replace it asap
 
Some ideas to check on:

1. Ensure Kyber crystals are correctly warming up
2. Flux Capacitor is topped off with ONLY GENUINE Chiquita Bananas
3. Skyactiv Blowoff Valve is working properly.
 
Our has the whine too. Stops about 30 seconds after ignition off. I assume it's normal. It has been pretty consistent and has a clear "click off" sound. I don't know what it's for though.
 
Our has the whine too. Stops about 30 seconds after ignition off. I assume it's normal. It has been pretty consistent and has a clear "click off" sound. I don't know what it's for though.

It's normal. Older Mazdas do this as well
 
If it's like a buzzing sound then from memory its the cat converter powering down
 
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