What is the toyota sienna humming noise?

If the Toyota Sienna is having a humming noise when You are driving then it can be a couple of things. The most common is the tires cupping. Tire cupping happens due to uneven wear in the tires. As You drive the lower parts of the tire bounce and scrape on the ground, which will sound like a humming sound. This will not go away unless You get new tires. It is not immediately a problem, but it will continue to make the tires wear more and more. If the sound gets worse when You get to a higher speed then You have an issue with the wheel bearing, and they are rattling in the sockets. This will need to be fixed right away, as being ignored will lead to additional problems.