The brake pad has become unstuck from the caliper. Easy 15 minute fix.

 

Out of curiosity, how do you know? Is it because of the noise or how close the brake pad is to the rotor?

Is the caliper tool needed to do this? I've changed the brake pads on my Xterra and didn't need one and it was easy. I actually have a german caliper tool for this, but I'm afraid I'll screw something up.

Is it still safe to drive?

 

I had the same problem. It was mostly around 25mph. Its safe to drive. You just need to pull the caliper off and restick the pad onto the caliper.

 

How did you know which wheel it was? I tried jacking up the wheel that I thought was making the noise then rotated the wheel around, but didn't hear any strange noises.

 

I just replaced all my brakes, because they were due. You need to push and pull on the pads to find the loose one, rather then rotate the wheel. Bumps are what make the noise.