Good Afternoon:
After reading your answer to the woman with a 2009 Toyota that’s making a strange noise while parked in the garage - potentially being an emissions control problem- Id like to contribute my own thoughts.
I think she’s hearing the multi disc changer in the trunk of her car. They tend to rotate the disks every so often. After parking for the car for a week or more- they’re also known to sometimes drain your battery.
I hope this helps!
Lorie 
This topic should probably be moved to the “The Show” category…
Whether this thread is moved to “The Show” category or not, I believe that I may have the answer to that person’s problem.
In the Owner’s Manual of my friend’s 2008 Rav-4, there is a notation about a self-test that the Evaporative Emissions System will run periodically, after the car has been shut down for several hours. This self-test involves a small electrically-powered pump, and the Owner’s Manual states that, if the owner hears a noise emanating from the central, underside of the car after the engine has been shut down for several hours, the noise is merely this normal self-test, and is nothing to be concerned about.
It’s amazing what one can learn by simply taking the Owner’s Manual out of the glove compartment, and reading it.
;-))