Oil or butter your slow cooker insert. From the author of this recipe: "Trust me, don't skip this step...you'll hate yourself later if you don't." I think this step is quite important.
Add the beef to the slow cooker. In a large bowl, mix together the canned soup, gravy mix, and soup mix with 4 cups of water, pour soup mixture over the beef.
Cover and cook for 6-8 hours, looking for very tender beef.
About 30 to 90 minutes before serving, turn the slow cooker to High setting, add the mushrooms and egg noodles.
For the egg noodles, if you have frozen egg noodles, add them as is, frozen, with the mushrooms. If you only have dried egg noodles, cook those in a pot of boiling water until just before tender, drain, and add those.
Stir and squish down the noodles so they are covered with the liquid. Cover and continue to cook on High setting for 30-90 minutes to either cook the frozen noodles or heat through the cooked noodles.
Serve.