2006 Saturn Ion noise

Noises like that often sound like they're coming from the transmission but that is rarely the cause. The common causes are wheel bearings and tire wear due to misalignment, or possibly a broken belt. Broken belts are typically also felt as a shimmy in the steering wheel or a wobble in the seat. Front wheel bearings almost always cause a steady drone or buzz like an airplane engine. Rear wheel bearings can sound like you described but that type of noise can resonate and sound like it's coming from other areas of the car.

There is a tool you might be able to borrow or rent from an auto parts store that borrows them called the "Chassis Ear". It is a set of six microphones, a switch box, and headphones. You clip the microphones to suspect points, then drive around while listening with the headphones. You can move the microphones around to zero in on the source of the noise. Be aware that many mechanics have never seen or even heard of this tool. Suspension and alignment mechanics use it to find rattles, squeaks, and other noises.

The mechanics at tire and alignment shops are good at finding noises. It may be faster to let them find it, and less expensive than replacing more unneeded parts.

Various stores in different cities borrow tools. By me we have an O'Reilley's and an Auto Zone that loan them. There may be others too.

You can also find this tool on the trucks the guys visit the shops with each week. I like Mac Tools and have a lot of them. Matco is also very good, and there's Snap-on and Cornwell. Those guys get $200.00 for the original Chassis Ear with six wired microphones. You can search their web sites too. There's a newer model that has two wired microphones and four that are wireless. I don't know the price for that model.

I've also found listings for these on Amazon as low as 70 bucks.