I'm a new 2500 4X4 Auto Cummins owner (3 weeks) and have a question about a strange noise the truck makes between 1600-1900 rpms: Around this rpm range, the truck exhibits a moaning or whistle/ringing noise from beneith the passenger area. I can't tell if it's exhaust or transmission. It sounds like someone blowing across the top of a beer bottle, but higher pitch. Or, the sound made when someone runs a wet finger around the top of a wine glass. It sounds like some type of harmonic, but it only occurrs in that rpm range. Inside the cab with the windows closed, I first thought it was a faint siren. With the windows open, it's very clear. I guess I would like to know if this is normal and just a characteristic or if this is a known issue, perhaps with a remedy. Other than that, I love the truck!!!