Van is making a noise?

My van is making a noise that I’ve never heard before in a vehicle. It only happens after I’ve driven about 10-15 minutes. It happens when I slow down to about 10-15 MPH and stop and then when I start to go again until I hit about 20mph and then it stops. I recently had my back brakes changed and my mechanic originally said the noise was because my rotor was warped, and it would eventually stop making the noise, but it’s been over a month now. I tried adding a video of the noise but I’m not seeing that it uploaded. The best way I can describe the noise is to sound like something needs oiled, sounds like it’s coming from one of my wheels.