Bring a large pot of water to a boil, then salt generously. Cook the pasta until al dente. Drain and reserve.
In a large bowl, stir together the mayonnaise, sour cream, cider vinegar, mustard, sugar, pepper, dill and salt.
To the bowl, add the drained pasta, ham, grapes, cheese and green onions. Stir to coat with the dressing.
Cover and chill for at least 6 hours, preferably overnight.
