Cook the pasta in a large pot of salted boiling water for 7-9 minutes until al dente. Drain and rinse under cold water to cool.

In a mixing bowl, toss shredded carrots and onion with apple cider vinegar and marinate for 15 minutes in the refrigerator.

Combine mayonnaise, milk, and sugar in a separate bowl; whisk until smooth and creamy.

In a large mixing bowl, combine cooled macaroni, marinated vegetables, and dressing. Fold until well mixed. Season to taste with salt and pepper.

Cover and refrigerate for at least 4 hours to allow flavors to develop. Stir before serving.