What would make a grinding sound in my Ford Explorer?

I just replaced the brakes a week ago thinking that was the problem. Wheel bearings were replaced a couple of years ago. Haynes repair manual explained how to check drive shaft and u- joints, all ok as far as I can tell. Next thing would be cv joint universals. Is there a diagnostic check to rule this out as a problem. I'd like to eliminate all potential sources before having a repair shop do this later. Could wheel bearings go in just a couple of years? Usually they howl when bad, but can they make a grinding noise?

Thanks for all constructive responses.

Year of Explorer is 1997.What would make a grinding sound in my Ford Explorer?
Yes, wheel bearings can go in just a couple of years, I always recommend installing a USA or OEM brand of wheel bearings, the chinese brands just don't have a high enough grade of steel to be riding the weight of your car on.

A grinding noise can be produce by the wheel bearings, however it depends on when you hear the noise.

If it is produced when braking, it will most likely be a problem with your brake pads, caliper, or rotor.

If the grinding noise varies with Speed and possibly steering (slight left or slight right) this would put it more into the ball park of a wheel bearing, and if it varies with RPM, you are in trouble as you have engine or transmission issues, however it could be as simple as a belt or pulley.

Premium wheel bearings can be purchased from http://mibearings.com if that turns out to be the issue.

Good Luck!What would make a grinding sound in my Ford Explorer?
Wheel bearings can last the life of the vehicle in many cases so if yours were changed recently I'd doubt they're the cause. Usually the first signs of CV joints on the way out is a thumping in the joint when turning sharply. You can sometimes check the CV joints by jacking up a wheel and holding your hand tightly on the boot have someone turn the wheel both directions and feel for play in the joint itself. Assuming yours is a 4WD since you mention CV joints, maybe you can isolate exactly what seems to make the grinding noise as far as driving conditions. Is it related to steering, acceleration, braking or just routine driving?