My 2006 Toyota Sienna has started to make a loud humming sound. I took it to the mechanic and he suggested changing the timing belt but the sound did not go away continues. The sound speeds up the faster I drive and stops when the van is stationary. I have an audio recording but did not find a way to upload the file here.
Tires are usually the cause of these types of noises. Especially old tires. Not worn, old. If any of tires have been on the car for over 6 years, say the rears, they may need to be replaced even though the tread isn’t worn out.
Ask the mechanic to check your wheel bearings in case he didn’t.
If the pitch or volume of the hum changes when the steering wheel is turned off-center (i.e. changing lanes) that may indicate failing wheel bearings.
The answers seem to cover the ground well. My response initially was “Maybe it just doesn’t know the words.” But that would have been too silly, so I didn’t say it.