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