Humming/buzzing noise in 2020 SR5

Just a crazy question for everyone.....I have been noticing this faint buzzing noise from the underneath rear part of my garaged truck late at night on a day I have driven it (which isn't that often). Wondering what it could be since I'm an old guy and not tech savvy. Is this something the truck does normally or is Toyota downloading driving information? It comes on and goes off on it's own. The truck just had it's first service and all was okay. This has happened three times now that I've noticed....once before the service and I forgot to ask them about it. I was so focused on getting the TSB transmission upgrade which they declined to do saying they couldn't get it to show it needed it.

 

Normal noise, its in the Owners Manual.

 

It’s the evap system testing and purging. Completely normal.

 

Thanks for the answers....that's a relief and sure makes sense. Didn't think to check the owners manual

 

That's for sure.....almost immediate. I've only covered the important parts of the manual for safety features, necessary stuff and maintenance. That little TV on the dashboard is way over my head so I just listen to the radio and occasionally plug my wife's phone in for some good bluegrass on Iron Horse Radio