Cook the pasta by boiling salted water and adding ziti for 8-10 minutes, then drain and rinse under cold water.

Prepare the vegetables by finely dicing the red onion, red bell pepper, and celery, then mix with celery salt, celery seed, and diced pimentos.

Add the grated carrot to the vegetable mixture.

Make the dressing by whisking together sour cream, mayonnaise, and white sugar until smooth.

Combine the vegetable mixture with the dressing and then fold in the cooled pasta.

Incorporate the diced cheddar cheese into the macaroni salad.

Chill the salad for 4 to 6 hours or overnight before serving.