battery fan noise or something else?

driving home last night i noticed this strange noise coming from the back seat area. not very loud, just a faint electrical motor sound emitting from the passenger rear side of the vehicle.
It was strange as in i've never heard it before, i eventually narrowed it down to what i think is the battery fan. When i stopped and got out with the car still running i went to the back seat and listened under the seat and could hear the fan running.
What I thought was strange though was the noise when driving. I would only hear it at speeds above 20 km/h. When i would pull up to a stop and slowed below 20 the noise would switch off, no change in pitch, it would just stop. Then when i would accelerate above 20 the noise would "switch on again". I was only driving through an urban area at the time so never got speed up to anything faster than 50kmh.
I'm used to the typical regen braking noise, inverter whine, brake popping noises, etc but this one has me a little worried as it was a new sound and it was coming from the battery area.

I do live in a very hilly area with lots of short steep hills that usually gives me full bars on the battery at least once a day. Also rush hour traffic can be horrendous around here which can bring the battery down to 2 or 3 bars sometimes.

Is there anything else in the rear end of the v that could be making funny noises?

 

I heard it again today. Happened in the exact same place it happened the first time. It does the same thing, gets louder as i'm driving faster then "switches off" when i come to a stop. was 44f and at night when it happened the first time and 55f and sunny when it happened today. lots of hilly driving again.

Like you say I do not understand why it would switch off or become quiet when slowing down. i would think even when stopped the battery would need to cool off if it is hot.
I always have the cabin set to a cool yet comfortable temperature as from what i understand the outside temperature shouldn't affect battery temperature directly if the cabin is cooled by the ac. does that sound right or are other factors at play?

 

Does this battery fan have a vent to the outside? does it suck in air or blow it outside? perhaps the extra noise i'm hearing is the fan blowing air through the vent opening and at higher speeds i hear some extra wind/road noise through the vent to the outside?
As for the hilly driving, its all very new to me, I just moved to the coast less than a month ago from the flatlands of edmonton so hills and city driving are all a new to me and my v. I suspect I'll have to get used to this new noise.

 

I can see this being a problem here as the days get longer. My parking spot at home is outside and on the right side of the street facing west, so on a sunny day i'll be getting all that afternoon sun heating up the interior. Might have to get one of those sun shade things from the accessory shop.

 

Getting used to the noise now as I hear it on a daily basis. It doesn't really "switch off" as i put it in the original post. Just changes pitch/sound level rapidly when coming to a stop. I can still hear it faintly while stopped(car still in ready mode).
If it does exhaust through the spare tire well it would still technically be exhausting air outside as there are drain holes in the spare tire well so some air would be forced out of there, besides the vents in the rear hatch/trunk that encourage fresh air from the front vents to flow through the vehicle. So maybe what i'm hearing is a little extra wind noise from the outside as the fan is running forcing a little more airflow through the vehicle?

Or maybe I'm just way overthinking all of this.

 

Ok well I heard the fan change speeds today while cruising on a flat section of road at 50kmh. It was loud for a few seconds then switched to a lower speed while driving along at the same speed. Seems my earlier experiences were merely coincidences that the fan speed changed as I happened to roll to a stop.
It also could be a case of the electric motor pulling power from the battery for propulsion so requiring the fan to run for cooling, and when rolling to a stop at low speed, friction braking takes over completely giving the battery a break and chance to cool down, hence the switch to lower fan speed.
All makes sense now, I understand its not road noise I'm hearing, just a cooling fan that at its highest speed can sound like a small airplane taking off

 

I actually live in north vancouver, much steeper/hilly than downtown or most of the lower mainland. my residence is 300 meters above sea level. 5 km down the road i am at sea level. Lots of stop lights in the middle of all these steep climbs and descents.

As for my driving style, i try to drive smoothly anticipating stops, accelerating just below the pwr zone when possible to keep up with traffic.

I'm pretty sure quick charging the battery to full bars with regen braking generates alot of heat. Often I notice after a long descent and full charge on the battery at a stop light the engine will keep running, though sometimes i can press ev button to make it shut off. Though as soon as i try to accelerate the ICE will start very early and override ev mode, i'm sure this is to protect the battery from heating even more by drawing power for propulsion. A minute or so later though all that extra juice comes in handy for powering the AC to cool the cabin or cruising around town in ev mode. I think my next car will have to be a plug in. I'd only need to charge it to 50%, the rest of the charge would come from my downhill descent to work every day.