"brrring" sound when truck is off?

I'm not sure how to explain this:

It's a 2011 Tacoma, 4WD, 2.7L access cab, 75K miles. I've also got a hearing aid.

Several times I've heard a single 1/2 second or less "b-ring" or "brring" or ring sound a minute or two or longer after turning the engine off. If I'm in the truck, it sounds slightly faint. I've heard it outside with and without the driver's door and access cab door open. It doesn't happen all of the time and it's only after the truck is turned off .... and a minute or more at that. Sometimes the alarm is engaged and sometimes it isn't.

It doesn't sound like my hearing aid, cell phone, or anything else. I had a friend ride with me once, and it didn't happen even though we sat in the truck, and waited outside. It's unpredictable, but it is also loud enough to hear with my hearing.

Any thoughts or guesses?

 

Smog pump.

 

Aww, video?! LUCKY.

 

Thanks. Would one expect it to make a one-off sound a minute or more after the engine is off? And, not each time, either?

I'm guessing it's the sound at :02 in the video - minus the engine noise and thud. Heard it again today, more like a <1 second short bell ring, and loud since was standing about 10 feet in front.

 

I'm thinking it is more likely to be the evaporator pump at the back. Its a faint whirring that can kick in any time. The vacuum cleaner sounding air pump up under the hood only runs when the engine is cold in order to feed more air (oxygen) to the exhaust manifold to continue burning the rich startup mixture and reduce emissions.