I did a search, but nothing quite explained the situation we're having with my fiance's 2004 Cav.

There's a vibration coming from the front end, above 65mph, but ONLY when you turn the steering wheel slightly to the right (as in lane changing, gradual curves in the highway). There's no vibration when driving straight, nor is there when changing lanes to the left. The vibration itself isn't very rough, just a pulsing feel you can feel through the floorboard and wheel. It's also rhythmic. Any ideas?

Go see this subject you will probably get your answer, i think it is a wheel bearing: Wheel Bearings? Brake Pads? werid front end sound.

Actually, I think it's the opposite, as the vibration only happens when turing the steering wheel to the right. It may be the wheel bearing, but I'm thrown off by the fact that it's only when I turn the wheel slightly to the right.

Rotate you tires and see if the noise moves to the rear of the car. If it moves then it's possibly something to do with the tires. They may also be out of balance.
I would also have said wheel bearing, i replaced my drivers side one a little while back and after i did it the Tech who helped me do it said he thought that the right hand side one was also on its way out and i notice that i get the noise at exactly the same point, (highway speeds while turning slightly to the right) as you do.



(99 - Sunfire - Red - 2200)(95 - Cavalier z24 - Purple - 2.3 quad four)

I agree it sounds like the wheel bearing. I had that exact noise on my 99 after I bought it used. The dealer said they would fix it but they replaced the wrong one. The way you turn to make the noise is not necessarily the side that has the bad bearings apparently. I changed the other side myself since the assembly is around $80 and the job is not too bad with the right tools.