Its possible for the noise to only happen at certain speeds. The best way to test the wheel bearing is by driving the car. Drive it at the speed the noise occurs. Turn slightly in each direction. If the left bearing was bad, it would get worse when you turn right, because you are loading the bearing.
If you are testing this on jack stands, you need to turn TRACS off. The TRACS system is not in the transmission at all. Its simply part of the ABS system and it brakes the wheel that is slipping to apply power to the wheel that is not.
If you felt a rough spot on the bearing, that is cause for concern. There should be no rough spots. You can run it with no axle but keep an eye on the fluid.
You need to understand that I cannot hear the noise online. I can only tell you common causes and some checks. I have never had a trans make a noise (though it is possible) and I have replaced many wheel hubs. Also, the bearing is the cheapest of the three (bearing/axle/transmission). So if I were to guess, based on symptoms and cost of guessing, I'd guess the wheel bearing. If you want to be sure, you might consider having it professionally diagnosed.
A hub will run between $85 and $190 here. Its the most common cause and the cheapest and you feel a rough spot, so it might be worth taking that guess rather than a $5000 transmission guess or $500 axle.