Whistle/high pitch faint whining noise with key in ACC position

Hey guys, probably nothing but I was updating my radio head unit last night and had the key in the ACC position for about 15mins while it updated. Noticed a faint high pitch whistle/whining noise that seemed to be coming from under the jeep around the firewall/bell housing area. Constant faint noise that didn't change or stop until the ignition was turned off.

Different than the initial sound the fuel pump makes when it primes and HVAC was off. Probably always been there but just curious if anyone else has noticed this or if my JK is about to self destruct, .

My first thought was the vacuum pump, but that's up front by the bumper.

Does it run when the key is in the acc position ?

.

Yeah, seems more under jeep back near the firewall and rear of the engine. I did wire up an ARB compressor this weekend but the noise isn't coming from any of that (not the related compressor relays, switches, wiring or battery) so I don't think it's related. Only notice it in the ACC position (engine off), faint whistle. Reminds me when a relay isn't getting enough current and makes a little noise. Probably nothing.

2014 JK for reference.

Pretty coincidental I have a 2013 JKU and noticed that same sound last night while downloading music to the built in hard drive of the factory stereo, I thought it was my beer fridge. If I had to guess it sounds like a noisy power supply or transformer, definitely electrical.

probably the canbus, it emits a high frequency noise in some of the components. nothing to worry about.