if its a rear wheel chock the other side's wheel (bricks?) and put the car in gear.
pop the suspect wheel off the ground, and support the car safely,
spin the wheel by hand to see if you can see what the noise is.
if you cannot see the conflicting parts, remove the wheel (may need to put it back on the ground to undo the wheelnuts)
try spinning the hub, listen for noise, and again try to hear where it is coming from.
if you still have noise...
Disc brakes: (always fitted to the front) maybe it is a brake pad worn (to the metal?) or the pad material has unglued itself from the metal backing plate.
Drum brakes: (different to the front brakes, like a bowl with 4 holes) the brake shoe material is either worn or off the backing plate.
If it does sound like the brakes they may need replacing, if you're handy with spanners, its not too bad a job.