1995 Mercury Mystique transmission question

1995 Mercury Mystique mileage 132,000. Recently our Mercury Mystique started making a noise from the left front wheel, since it sounded like a bad tire I took it to the local tire store. After driving it they put it up on the lift and they showed me that while spinning the left front wheel you could hear a clunking noise inside the transmission. They said that they thought I should have the transmission checked out. They also said that my left front wheel bearing housing was bad and that was what was making the noise, but they suggested that the bad bearing was caused by the transmission. What inside the transmission would cause the bearing to go bad? If I decide to rebuild the transmission myself, how hard is it on this car and will I be able tell what is causing the noise when I get the transmission open? Is there a book that you would recommend that may help me?