Cook the macaroni by bringing a large pot of salted water to a rolling boil. Add elbow macaroni and cook until al dente, about 8-10 minutes. Drain and rinse under cold water.

Prepare the creamy dressing by combining mayonnaise, sour cream, lemon juice, and Dijon mustard in a medium bowl. Whisk until smooth, then add dill, onion powder, salt, and pepper. Adjust seasoning as needed.

Combine the cooled macaroni with diced red and green bell peppers and diced celery in a large bowl. Add cooked shrimp.

Dress the salad by pouring the creamy dressing over the macaroni mixture. Toss gently until well combined.

Chill in the refrigerator for at least 1 hour or overnight before serving. Stir in extra mayonnaise or sour cream if needed before serving.