Could be several things, may be hearing the little motor that opens or closed the active grill flaps, the car also has an electric water pump that cools the battery and electronics or cooling fan on the radiator.

 

I noticed this sound in my car and it turned out to be the seat ventilation, if you press the warmer button next time check if you can see that on (you might not be able to feel it but you can certainly hear it)

 

Thats the noise that even confused the Hyundai mechanics whilst trying to sort out a different noise on my car - see below

 

It's coming from the section that has all the HVAC controls and buttons.

 

If you have very sensitive ears....and air conditioning is running you are able to hear refrigerant in the line's passing over expansion valve.
This valve has function to control pressure difference that is necessary for healthy air conditioning operation.

 

Here is the sound Weird hissing sound ioniq 5

 

I've noticed the same noise from my i5 2022 AWD (Canadian Spec); dealer "inspected" when in on scheduled service and determined the noise as "normal".

Don't agree with their assessment, but also not confidant enough in the dealer to further investigate and not ruin something else in the process.

 

My 2020 Hyundai ioniq ev I had it for 2 weeks running fine then one day I charged it to 80 percent then picked my wife up was going good until I almost got home there was hissing noise coming from front passenger side and I was keep on driving to go home and call Hyundai about this then my ev light pops up then 5 mins later the ev shuts down no power I would have to push the botton to shut the computer off then start back up and the ev light is gone put it in drive hissing starts up 5 mins later ev light pops up and same thing happens so I did run a 12 volt test I am getting the volts it needs but I just don’t know what the heck this sound is when it’s in park or u stop at light it shuts up hissing when u have it in drive or reverse it starts hissing I called Hyundai they can’t look at it till Oct 6 th which is too long of a wait for me I took to a local mechanic and they can’t even pull up the code if someone out there can help me I appreciate as I really love driving the ev more then my gas car

 

I believe this may be a snake attracted by the electrostatic electricity in the car (this happens in Australia). If so, it's difficult to recommend a solution other than to make sure you don't go far from a hospital which has anti-venom to suit the snake concerned.