Place onions in a 4-quart slow cooker; place roast on top. Add beer and next 4 ingredients.
Cook, covered, at HIGH 8 hours or until roast is tender. Remove roast and onions, reserving drippings in cooker.
Whisk flour into reserved drippings; cook 10 minutes or until thickened. Serve with roast, onions, and hot noodles.