Replaced rear pads/rotors now a grind, possible wheel bearing?
 

Im dealing with an 03 Camry, it is my wifes. She was complaining of a strange noise that sounded like a very faint thump, almost like a tire sounds if its going flat(no, its not flat) only when driving on the highway at 40+mph. I checked everything out and noticed her rear pads/rotors were worn down to the metal(150k miles, alot of mountain driving, original brakes). I replaced those today, now I notice a metallic grinding that I didn't notice before.

I backed the (parking)brake shoes all the way off when I removed the rotor, I spun the hub freely after I removed all the brake hardware, and heard no grind, but as soon as I put a rotor on and spun the hub again, I would get the grinding noise. I don't see anything rubbing, I even tried adjusting the parkingbrake shoes in and out and it did nothing to help the noise, but as soon as I remove the rotor, the hub doesn't make any noise when spun. Would me putting the rotor on the hub be enough to make a bad bearing make noise? Im not wanting to spend $250 on a new hub only to find out it could be something else... someone help me out, Im driving myself nuts thinking I did something wrong here.

And btw, the noise my wife originally heard is still there, she got so tired of listening to the noise that she just kept the music loud lately, so she can't say wether or not she heard a grind before I did my driveway repairs.

I have to ask if you put the pads on correctly? As in the pad part rides on the rotor and not the metal backing.

How about the shoes, are they now riding on the drum part of the rotor? Is is possible a a spring or something in the emergency brake system is now riding on the rotor/drum.

Is the sheet metal splash plate bent (large round or half round plate that keeps water off the drum)? This can get slightly bent and cause a grinding noise as it contacts the rotor (a common issue after working on the brake system).

If none of the above, try installing the caliber without the pads installed and determine if the grinding is still there. Of course DON'T apply the brakes or you will push out the brake pistons.

Doubt if a bad wheel bearing would now make more noise after the rotor was installed. If this was the noise source you should be able to hear it when driving due to the extra load now on the bearing. Try making slight turns left and right when driving to shift the cars weight from one side to the other. If a bearing the noise may get louder or softer as the weight is shifted on and off the axle.

As to the thumping noise. Check your tires carefully. One of them could be damaged, starting to have a ply separation, etc.

The grinding starts as soon as i put the rotor on and spin it, before I even put the caliper bracket back on or anything, let alone the pads or caliper. That is what makes me wonder if just a little pressure applied to the bearing causes it to make noise, because if I pull the rotor back off, it doesn't make any noise. I checked the splash guard and it was not bent. I checked that the shoes were properly seated, which they were. I guess next to check is any springs that could have jarred loose. Other than that, I really dont know what else to check. I guess I will have to tear back into it tomorrow after I drove it about 10 miles tonight, maybe if anything is rubbing it will leave a mark on the inside of the drum part of the rotor.

If you think it is a bearing, try mounting the tire and spinning it (without the rotor installed). This would really increase the load on the bearing.

Is the grinding constant or does it come and go, get louder and softer. If not constant would suggest something is rubbing.

The fact that the problem is at 40 MPH would lead me to check my tires for a tread separation bubble. Have discount tires check the tire.

or

If you have aftermarket rims check to see if the wheel requires a load centric hub to properly center the tire. This fixed a similiar problem on my Honda Accord.