Identify this vibration source in my Dakota

99 dodge dakota slt extended cab. 51k miles.
There's a mystery vibration noise that I'm trying to locate. Maybe you can help me find it.
I get what sounds like some sort of metallic vibration noise at around
35-43 mph, but only AFTER the truck warms up. It sounds like a harmonic "whine". It might be something metal vibrating at high rate rubbing against something else that's metal, but that' s just a guess. It's not particularly loud, just enough to be annoying (and no, it's not tire hum - it's higher pitched than that).
The noise seems to be coming from the area just behind the cab where the gas tank is on the driver's side. I've crawled under there several times and haven't been able to find anything.I thought maybe it was a heat shield on the gas tank vibrating, but I stuffed some rags under them to test, and it still did it. The noise only occurs when the truck is in drive. It won't do it at all when in park. If you let off the gas, the sound stops, so it's not a wind-caused noise.
I would think maybe the exhaust, but the sound seems to be coming from the other side of the truck.
Any ideas? It's driving me crazy!
thanks
Todd
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On 14 Dec 2005 14:18:10 -0800, todd snipped-for-privacy@hotmail.com wrote:

Universal Joint(s) ??

"Leroy"
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catalytic converter, i had mine replaced, sounded like a piece of metal vibrating on metal. get someone to rev the engine and listen for it.

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