Cook the macaroni according to package directions until al dente.
In a large bowl, mix together the cream of chicken soup, cheddar cheese, gruyere cheese, mayonnaise, sour cream, onion powder, dry mustard powder, and pepper.
Stir in the cooked macaroni until well coated.
Transfer the mixture to a greased crockpot and cook on low for 2-3 hours or until heated through and the cheese is melted and bubbly.
