Fixing Whirlpool Oven Fans and Doors
I think your reasoning is good - it's pretty easy to pick out a the sound of a fan hitting against something. I recommend RepairClinic.com. They have a great site for appliance parts, and lots of info and schematics for what parts are available and how to replace them. You already have the manufacturer and model number, so you are ready to go.
Hope this helps.