Cook the macaroni according to package directions until al dente. Be sure not to overcook it, as you want it to be firm in the salad. Once cooked, drain and rinse with cold water to stop the cooking process.
While the macaroni is cooking, chop the onion, celery, red pepper, and hard-boiled eggs into small, bite-sized pieces.
Mix the mayonnaise, mustard, vinegar, pickle relish, sugar, salt, and celery seed in a large bowl. Stir until smooth and creamy.
Add the cold noodles, chopped veggies, and eggs to the bowl and gently mix everything until evenly coated with the creamy dressing.
Cover the salad with plastic wrap and refrigerate it for 2 hours before serving.
