Bring a large pot of salted water to a boil. Cook macaroni according to package directions, until al dente. Rinse with cold water and drain.

Cool the noodles completely before adding the dressing.

In a large mixing bowl, toss together cooked and cooled noodles onion, celery, bell pepper, and carrots.

In a small mixing bowl whisk together mayonnaise, sour cream, milk, cider vinegar, sugar, dijon mustard, salt, and pepper.

Pour half of the sauce over pasta and toss until everything is well coated.

Cover bowl with plastic wrap and chill for at least one hour before serving.

Stir in additional sauce before serving. Add a splash of milk, for a thinner sauce, if desired.