Cook macaroni noodles al-dente according to package instructions. Drain and rinse under cool water, drain again and transfer to a large bowl.
Add celery, pepper, onion, and shrimp and stir to combine.
In a separate bowl, whisk together dressing ingredients (mayonnaise, sour cream, vinegar, sugar, celery seed, ground mustard, salt, and black pepper). Taste test and add more salt or pepper as needed.
Pour dressing over macaroni mixture and stir well until all ingredients are coated with dressing. Cover shrimp macaroni salad and refrigerate at least one hour (preferably overnight) for the flavor to fully develop before serving. Always stir before serving.
