Cook macaroni in a large pot of well-salted boiling water until al dente. Drain the pasta and rinse until cool running water to quickly chill it.
Meanwhile, prep the vegetables and assemble the sauce. In a medium bowl, whisk together the mayonnaise, red wine vinegar, Dijon mustard, dry mustard, salt, pepper, and sugar. Use a microplane or the smallest holes on a box grater to grate in one clove of garlic. Whisk until combined. Taste for seasonings.
Toss the pasta with ⅔ of the sauce. Stir in the diced bell pepper, celery, carrots, onion, and dill. Cover and refrigerate both the pasta and remaining sauce for at least 30 minutes, or until chilled. Before serving, toss with the remaining ⅓ of sauce.
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Notes
Alternative chilling method: Because I know that some people don't like rinsing pasta until the water to chill it, another option is to toss the pasta with ⅔ of the dressing and the veggies, then chill in the fridge for an hour. The pasta will absorb more of the sauce this way. Toss with remaining sauce before serving. You can also toss the pasta with a bit of oil and chill it separately from the sauce, but this way the pasta doesn't absorb as much of the sauce flavor.
Storage: Keep leftovers refrigerated in a closed container for 3 to 4 days. I have not tried freezing this salad, but I don't generally recommend freezing raw vegetables as they lose their crispness during thawing.