Magnum SE rear end shimmy

[MacGeek]

So I've got this lingering issue with the Magnum that's making me crazy. Dealer says they can't reproduce it. I'm going to take them for a ride next time it's in to attempt to show them, but was wondering if the collective brain-trust here had any ideas.

2005 Magnum SE. Since new, I've had this shimmy in the rear end at exactly 35 MPH. 30 is fine, 40 is fine, and it's in the rear since I don't feel it in the steering wheel. Brakes don't pulse, all four wheels have been rebalanced - twice. I don't notice much vibration anytime else. The car's now got about 8500 mi on it, with the crappy Goodyear tires. I'm thinking it's gotta be an out-of-balance driveshaft, bent axle shaft or spindle.

Any thoughts?

[NC-SXT]

Rotate fronts to back. If it stays cant be wheels.

[UberPariah]

what type of road are you on? i know that when i am on the freeway and come upon a vertical grooved stetch of pavement, my rearend goes all over the place. but i am also going 70+, so that probably doesn't help much either.