Bring a large pot of salted water to a rolling boil. Add the macaroni and cook until tender, about 10 minutes, or according to the package instructions. Drain well in a colander and rinse well under cold running water until cool. Shake well to remove excess water. Transfer to a large bowl.
Once the macaroni is cooled, add the cheese, mayonnaise, celery seed, mustard, carrots, celery and onions. Stir well to combine and season with salt and pepper. Cover with plastic wrap and chill in the refrigerator until cold, at least 2 hours. Taste and adjust for seasoning with salt, pepper and mayonnaise just before serving.