Steady (non-scraping, non-metallic), speed-varying noise from frontend (possible rubbing brake pads?)

Car: 2006 Saturn Ion, front wheel drive.

Symptoms

A steady friction sound, like loud road noise (not a scraping, not metallic), comes from the front end, audible starting around 20 MPH, and getting louder with increasing road speed (unaffected by rev count). The sound basically goes away when going around a right bend (even a small turn of the steering wheel to the right drastically reduces the sound), and gets louder when going around a left bend. Turning the engine off while traveling has no affect on the noise. With the car parked and in neutral, no noise is generated.

I put the front-end up on jacks and removed the front right tire. With the car idling in 1st gear, the left tire turned but the right didn’t. The front end would still generate the noise. I removed the brake, and the hub + rotor (secured with the lug-nuts) would turn in 1st with the gear idling. Also, no noise generated. The hub wouldn’t wobble, and turned by hand without any noise and felt smooth (no gritty/sandy feeling). The hub would turn with less than around 1 ft-lb of force (checked by setting a click torque wrench to 1 ft-lb & placing it on the hub nut; it would turned the wheel before clicking).

The brake pads are still quite thick, and were replaced professionally about 1.5 years ago, along with the rotors.

Steps Taken

• Swapping the front wheels had no affect on the noise.
• I tried out a new hub, and (with the wheel reassembled) the sound remained.
• In the process of putting the break back on, I recompressed the piston (with a c-clamp) and drained a little of the break fluid (and then topped off the reservoir), which ran clear.
• I cleaned and lubricated the brake pad clips (they were quite dirty). This may have decreased the noise at faster speeds, but it’s still quite present (especially when bearing left). (I’ll likely end up replacing the clips.)

From what I can see (and have read), the calipers are auto-adjusting (which is to say, not adjustable).

Questions

What other diagnostic steps can I take? Given the above information, what are the likely culprits, and what can be done?