Place the macaroni noodles on the stove with water and cook until al dente.
While the noodles are cooking, in a large bowl, mix together the chopped celery, onion, relish, mayo, mustard, vinegar, sugar, salt, and egg. Stir several times until the sugar dissolves into the mixture.
Remove the noodles from the stove and rinse with cold water until the pasta is cooled. Add the noodles into the bowl of salad dressing, Stir and coat the noodles well with the dressing.
Refrigerate the mixture for several hours before serving so that the pasta can soak up the flavors. Serve cold.