Even after replacing the brake pads, I hear a scraping or grinding sound as the wheels rotate, one scrape/grind per rotation. It’s particularly noticeable when I turn left, but the sound seems to disappear when I turn right. The mechanic said he doesn’t hear it, but I think that’s because he must have driven it on a gravel road. What else could be causing this noise? I worry that I’m making the problem worse by continuing to drive it.
Check to see if the brake’s backing plate is scraping the rotor or inner wheel. You should be able to see bright metal where it’s scraping if it is.
Could be rotors with significant runout.
Could be rust on the rotor, particularly if different types of pads were used prior.
Could be a bolt came out and the upper part of the caliper is rubbing (thought that would be more constant).
Could be a tire rubbing if the lug nuts are loose.
Could be a bearing or axle.
Could be a lot of things.
Try this, at a speed where you can here it rubbing, gently press the brakes. If it goes away while pressing the brakes, then it is somewhere in the rotors/calipers/pads. It the noise persists, then move towards tire, axle, bearing.
Try jacking up the wheels one at a time and spinning them by hand, induding doing so while the wheels are turned. If you cannot confirm anything, try removingg the wheels and turning the hubs one by one by hand. Bad bearings can show up as roughness when turning the hub when jacked up, but be “damped” by the weight of the wheel. Bearings can and do express themselves as your symptoms.
You should be able to tell if a bearing is bad by jacking up the car and trying to wiggle the wheel while watching for free play in the hub area. If there’s play in the hub you have a bad bearing.
If the wheel wobbles you do have a bad bearing, but you can also have a bad bearing without the wobble. IMHO the best way to check if there is no wobble, and no grinding sound is heard when spining the wheel, is by turning the hub by hand with the wheel off