04 rear end whine?

[Thoennes]

04 short bed 4-door 2500 with 6000 miles. since truck was new it has had loud whine at 45 and 50 mph. it goes away when i let off pedal and coast. no whine at lower or higher speeds. when i had first oil change in june i told the dealer about it and they drove it and said it whines. so they put additive in and said drive it. [it is an open rear end ]. talk to them today and they want me to bring it in so they can pull cover and check it out. i don't know if i want someone touching this truck because of all the stories i have read about on here about these rear ends. i guess i am saying i don't want a worse problem then what i have. are there people at dealerships that know how to set up a rear end?warranty means nothing when you need your truck every day or if it makes more noise after they work on it. should i or shouldn't i?well i have 3 days to make up my mind weather to let them mess with it or leave it alone and turn up the radio. thanks for the vent jerry