I found out that the problem was the idler pulley on the drive belt. The clip holding the pulley in place had broken. The pulley stayed in place, but began to squeal. I replaced the idler pulley arm, because I wanted to make sure there wasn't a worn idler pulley shaft causing the problem. I also found a badly worn front drum seal and replaced it.
The repair wasn't difficult. It just took time to disassemble the dryer and put if back together. I generally take my time and take pictures along the way. Removing the drum seal and gluing the new one in place took some patience and care. Removing the idler arm only required removal and replacement of one bolt once the dryer front panel was removed. After reassembly, the dryer worked great.