I can't help with your inability to read or understand anyone else outside of what comes out of your piehole.
The fan can go on after the ignition is off. The OP never specified if he was in or out of the car when he heard it.
I think the hood insulator is clogging your brain pan.

 

 

Sorry for the late response but was not sure how to respond basically to your response and some of your use of colorful words but to also give more and better information to help the OP and others that are reading and may have the same question.

Besides I think you are missing the point! And I doubt very much that you even understand how the fan system operates given you posted the fan general operation from an "owner's manual" not a factory service manual or guide and not the ECU programing that controls the fan and how?

I am also surprised if you read the first response and seem to know so much about fans that you did not suggest that the fan sound may also be the blower motor? Although I didn't dismiss that, and the OP really pointed more IMHO to the radiator fans that why I suggested looking for the hood insulator. The Mazda hood all is manufactured with the tabs for mounting it MADZA seems to only install them on some model not all of them. And it is not a factory option. You seemly have to know that one exists and that without it you are going to hear more sounds generated in the engine bay>

I recommend that maybe you go look and see if your MADA has one if not there are various after market companies that sell them which are much better at sound control, then the OEM MAZDA hood insulator!

 

Apology accepted, thanks.

 

I started a thread regarding the same issue with sound files attached.

I took my 2019 CX5 to the dealer for the same reason and he demonstrated to me that the sound is present in all Mazdas post 2018 or so and newer by starting and stopping a brand new 2023CX5 that was in their parking lot.
I was told it is the sound of the exhaust valve closing.

Try hitting the start/stop button without pressing on the break, you will hear it open and close loud and clear.

Actually, while the car is running, if you really concentrate, the sound is there and constant, just a little faint.

my exhaust valve failed at around 116000 km and the entire exhaust system was replaced under warranty (emission components have a longer warranty than the rest)

 

Change a few words to "like" or "similar" would be better. The OP in these threads needs a little more clarity and perhaps a different way to explain what is being herd because he stated in the first opening post for information the sounds lasted about 20 seconds. Your condition would be much less. So, let's see how the OP responds to a few of our comments perhaps with a bit more clarity in the descriptions before making it the exact problem as other may have had or you?

Honestly because it is so new, he should return to his dealership and have them look at the MAZDA and also maybe find someone at the dealership to give and better and more complete run through of all the MAZDA features how everything works. Very few people actually sit down anymore (if ever) and read the owner's manual when they buy a new vehicle.