I have an electric Affinity dryer that continues to squeak despite changing the belt, pulley unit, and rear bearing unit. The noise can be traced to the back of the dryer. I'm concerned it may be the motor. Any other suggestions?

There is not much more you can do yourself as far as troubleshooting. When it gets to a continuous noise, towards the back, the motor does come to mind first. Now, you would need to consult a Frigidaire service provider for an accurate and safe diagnosis before moving forward with any other decisions. If it is indeed the motor, and you have no limited warranty on that part, then consider purchasing a new unit with newer features, appearance, and standard manufacturer's warranty.

You have an idler pulley on the motor that is part of the belt tensioner. That is about the only thing I can see that would cause the squeak. You need to remove it and grease it with white lithium grease. Any other moving parts should also be greased with white lithium grease. Here is the manual: http://dl.dropbox.com/u/8010163/Frigidaire%20Affinity%20Dryer%20Service%20Manual.p df
This manual is no longer free online.