Goodman GMP 100-3 fan goes on and off by itself, with no request from thermostat. I even took the thermostat off and separated the wires, and it still happens. No specific pattern, just on and off sporadically. The fan that pushes the exhaust out the stack comes on as well, not just the blower. Any suggestions?

You may have a problem with the circuit board. I have put some repair manuals online for you to download at: http://dl.dropbox.com/u/8010163/Goodman%20Manuals.zip

This is unusual because there are two different relays controlling the two fans.