Today’s invention is a toy car set which is equipped with a pair of wireless headphones.
As the cars are moved by a child, the wheel rotation rates result in an appropriate-speed engine noise being generated (which would also mimic the correct engine note for each make of car, as well as gear changing and tyre squealing ).
Cars which collided with each other at a given relative speed would create a realistic crash noise level.
Other noises would include the closing of the toy’s doors…
…and all of this without disturbing neighbouring adults with incessant brrrming noises.