Cook the macaroni in salted boiling water 1 minute less than the package directs. Drain, rinse under cold water, and let cool completely.

Whisk together mayonnaise, sour cream, mustard, vinegar, sugar, celery salt, salt, and pepper until smooth.

While the pasta cools, dice the celery, bell pepper, and red onion into small, even pieces.

In a large bowl, combine the cooled macaroni, diced vegetables, and relish. Pour the dressing over and fold gently until everything is coated.

Cover and refrigerate at least 30 minutes. Before serving, stir the salad, transfer to a serving dish, and sprinkle with smoked paprika and fresh parsley if desired.