So I have driven the 2020 Corolla Hybrid for ~2.5 years now with a mileage of about 40k km. I am posting on this forum as I know the technology used for Corolla Hybrid and Prius are almost the same. I recently discovered that the hybrid battery fan located under the passenger rear seat needs to be regularly checked and cleaned. From my understanding, you are not supposed to be able to hear the sound of the fan running at any time except for when it is extremely hot. But I am able to hear it at (P) park. It almost sounds like the AC running at the lowest setting, but it is definitely coming from the back and my car does not have rear seat AC. I am not sure whether the sound is louder or not when I am driving as this car is not the most soundproof car out there and the road noises are louder than the battery fan itself. I am planning to take it to the dealer and get the fan cleaned and the filter replaced soon but I am just worried that the sound will not go away even after replacing the filter. I briefly explained the situation over the phone to the dealer after making an appointment and he told me that the fan running sound is completely normal for hybrids, but I am a bit skeptical. Is it supposed to be like this? Are the other Toyota hybrid owners out there able to hear the battery fan even at park?