Whine from rear of truck when parked

My wife noticed my truck making noise in the garage tonight. Sounded like a small electric motor spinning, most prevalent in the rear wheel wells. I drove it hours earlier. After I started it, it went away. Any ideas wth it could have been?

 

No worries. Modern vehicles do this . My wife's Lexus is doing all sorts of shit at night. SO does the Tundra. I dont worry about it because no appliance in my house has talked to me yet

 

Found post here pointing to the EVAP system

 

We have left both our vehicles for a month annually when we get out of Canada for some heat in the winter.....never had a dead battery

 

Yes, it’s the EVAP system and it’s normal. My Gen 3 and my wife’s 2022 4Runner both do it, usually 4-5 hours after parking them.

 

Key points about the EVAP system noise

• 
  When it happens:You might hear this noise a few minutes after turning off the engine, sometimes even several hours later depending on the car model and environmental conditions.
• What it sounds like:A hissing, clicking, or buzzing sound, usually coming from under the car.
• Why it's normal:The EVAP system is designed to periodically check for leaks by creating a vacuum in the fuel system, and this can sometimes produce audible sounds.

 

I only hear whining from my kids. Not the Tundra which does have it's normal electronic turning off after truck is turned off. Weird. I think

 

Yep, while we're sleeping our trucks are talking with the Toyota mothership, telling her all she's learned about us from the previous drive, compiling data, biding their time while they plan world domination.

But yeah, just the normal noises in here.

 

If the sound only happens when you stop and shift into park then it's the parking brake engaging. They are motor driven.
I never noticed it on mine until I had the windows down and put into park, & was "what the F was that"
This is normal operation.

 

The OP specifically said he heard the noise in the rear of his truck "hours after" driving it. This is without a doubt the EVAP system checking for leaks, not the electronic parking brake.