Ram 1500 vibration

I have a 2003 1500 Quad-Cab. It just turned 33,000 miles. Just last week, for the first time I noticed a humming or vibration when decelerating from
about 60 mph down to about 40 mph. That's the only time it does it, just when coasting down a hill in that speed range. If I give it a little gas going down a hill, it stops. The first time it happened I thought I had a flat tire, that's how loud it was. I have discounted the engine, tranny and exhaust form being the problem because I threw into neutral when it was doing it on another occassion and the vibration was still there. I am thinking driveshaft, or rear axle or maybe a wheel bearing. It is very difficult to isolate where it is coming from. I only have 3000 more miles on the warranty so I will be getting it over to the dealer shortly. The truck has run trouble free till now, and this problem sure isn't normal. I will let you know how it turns out as soon as I bring ot to the dealer.
Anybody else having a simlar problem with their truck?
Chuck
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I had a similar problem with my '96 and it was the pinion nut coming loose in the differential. This is very dangerous, because I didn't figure it out before the rear axle seized. When that happens the rear wheels just quit turning and it is very exciting. The pinion shaft gets sucked into the diff.. The driveshaft falls on the road and you are sideways in an instant. This completly wrecks the spool. The nut that loosens is a nylock binding nut. There is no safety cotterpin and castellated nut in the Dodge design. Steve

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