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Discussion Starter · #1 · (Edited)
Good afternoon!

I'm trying to determine if what I am hearing is normal hybrid stuff. I have a 2018 Accord hybrid touring, and I have noticed that during driving I get a noticeable high pitched "whistle" from the vent directly below the back seat leading to the hybrid battery.

If nothing else I have very specific information on how to reproduce the sound, however Honda technicians didn't really notice any sound, and when recordings of it are played they agree the sound is present, but that it doesn't sound like any real problem.

1) The sound is a very high pitched whistle that comes from the fan vent under the back seat.
2) The sound will come on only when driving at constant freeway speeds (60mph +)
3) If the speed drops below 60, the sound will immediately stop. I can NOT get the sound at anything less than sustained freeway speeds.
4) Under sustained freeway speeds, the whistle will appear, remain for anywhere from a few minutes to over 10 minutes, and then disappear for just as long. The noise appears to cycle on and off without any real rhyme or reason, but it does cycle.

My guess is that this sound is the cooling fan for the hybrid battery. I assume that the fan is always running, when the car is driving, but that perhaps the noise I am hearing is when the battery fan kicks into a higher speed. But it sure sounds like the fan has a bad bearing or something.

Are you supposed to be able to hear the battery cooling fan? And if it really is the cooling fan, why does it shut off IMMEDIATELY upon getting under 60mph? I would think it would need to continue cooling for a little while.

Thanks in advance for any suggestions!
 

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Noticed same issue on 2018 EX-L. Called dealership to see if this is normal...was told a service tech would get back to me but never did. Sounds like it's some kind of a fan and it cycles on and off. Sounds kind of like white noise. If it's normal it's not that big of a deal...just trying to figure out if it's normal or not.
 

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I am having the same issue with my 2019 Hybrid. It started at about 11,500 miles. I took it to the dealer and they replaced the IPU fan for the hybrid battery compartment. That seems to make the noise worse. They're suspecting that it might be the ductwork for that IPU fan. The fan sucks air from the passenger compartment through the vent under the back seat, middle. It discharges through a duct running along the right side back fender (behind the non-movable seat back) and into the truck through a small opening behind the right trunk hinge. I ran a fiber-optic scope down the duct and could not see anything obvious. It does look as if the way the ducting penetrates through the car body into the trunk might be the source of the whistle. The flange does not seal well against the body and leaves a few gaps. The nouse could be a while similar to blowing across a bottle. The dealer is ordering a new duct assembly and will contact me to return the car for installation when the part is in.

When I drove my carpool the other day, the larger passenger was sitting with his body covering that side bolster and the sound was totally muffled and almost inaudible.
 
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