Strange electrical noise from underneath the truck

For about 3 months now I will go out into the garage where my 2017 SR5 is parked and I hear a high frequency electrical buzzing / hum sound, and it’s happened about 6 times counting today.

The sound is definitely coming from underneath the truck, and between the back of the cab and rear differential. I found out after the first time it happened that turning the ignition on / off stops the buzzing.

So, next time it happens I’m going to crawl underneath the truck and see if I can locate the source of the noise. It’s loud enough that I can hear it from 6 to 8 ft. away, and it’s very strange as the truck had been parked for over 5 hours today when I heard the noise again. I had been in and out of the garage earlier this morning after it had been parked for well over 2 hours and there was no noise coming from the truck.

So again I turned the ignition on / off and the noise stopped.

 

It says in the manual it's an evap test. Also 90 other threads with the same question.

 

could it be the outside air vent opening?
If you have carista or TIS there's some option in it that after the vehicle is shut off a vent opens to let air in.

 

or that...lol
haven't heard of this evap test one but I know I've heard the vent thing.

 

yea, very spooky.....i will go into my garage a like 10pm, truck has been off for many hours and the evap test is running. what the hell does this truck just sit there and think of things to do on its own.

 

Good old EPA mandations...
Your truck tests the integrity of the fuel tank/low pressure system for fuel leaks or fuel vapor leaks. Most cars are required to do this now. Most cars use a small pump and pressurize or vacuum the tank down watch for pressure drops OR the amperage of the pump that's required to maintain a set pressure or vacuum.

 

Yes it's the evap test. It automatically comes on something like 4 hours after the engine is shut off. It's explained in the manual. Both my Tacoma and my Lexus RX350 makes this noise. It really baffled me the first time I heard in on the Lexus.

 

Thanks for the replies, and like I said the noise is coming from underneath the truck, and right in the area of the gas tank. I scoured both the owners and service manuals and did not find any explanation about this EVAP system test. So can anyone tell me where this test is explained in the owners manual.

 

Perfectly normal. My wife's new RAV4 does it too. Freaked me out the first few times too.

 

Like this noise? I had thought I left an air compressor on or something. Just the evap test.

https://www.tacomaworld.com/threads/buzzing-humming-noise-from-under-bed.474064/

 

I'm glad to find out it's nothing wrong with the truck.

 

My tacoma and scion do it.

 

Ugh- that would scare me too- in the olden carburetorated car days with my first car, I had a old BMW with an electric fuel pump that decided to stay on one day when I was away. The fuel pump continued to pump fuel and the float valve didn’t stop it, so it filled up the carburetor and ran down into the cylinders, eventually flooding into the oil pan and eventually leaking out of the engine onto the ground. When I came home, my mom told me that there was a leak under my car. I went out to look, and saw a big puddle of oily gasoline heading towards the gas pool heater which had a pilot light! Yup, hearing a fuel pump running on a parked car would scare me too.

 

I found this on page 8 of my 2018 Tacoma’s owner’s manual:
“Approximately five hours after the engine is turned off, you may hear sound coming from under the vehicle for several minutes. This is the sound of a fuel evaporation leakage check and it does not indicate a malfunction.”

Could this be the answer?

Edit: Just saw this same answer has already been posted. Never mind. Late to the game here.

 

Glad you posted this as my wife came in last night telling me that the truck was sitting in the driveway making a strange noise. Crawled under there with a flashlight and found where the noise was coming from..........glad I now know LOL

 

discovered that on my 16 a few months in. the unsettling part is that it is doing test or whatever it is while it is off, let alone the fuel system. when i discovered mine i was in the garage at 11PM, not comfortable with that in the middle of the night in my garage while i am sleeping.

 

Finally an answer to this. Honestly, its pretty annoying when you're trying to sleep in the bed out in the woods.

 

love this post heard that sound in my garage one day .Freaked me out thought it was something electrical in the walls of my house lol

 

Russian listening device.