Grinding noise from disk brake

I recently bought a Nimbus Oracle 27.5" unicycle. I really like it, but from the get go there has been a grinding noise coming from the disks when the wheel is at a certain position. At first, the sound was very soft, but after riding with it in the woods, the grinding sound has increased. Is there any way to fix this issue? Has anyone else experienced the same problem?

Can you describe the sound better.

Does it happen while you are braking, or is it constant (pulsing as the wheel turns)?

Most of the time when a new brake has a constant grinding noise it is because the caliper is rubbing against the rotor at one spot. The remedy is to reposition the caliper. This can be either a centering issue, or it may be that the adapter isn’t quite positioning the caliper correctly (new adapter, or possible shimming it with washers).

It pulses as the wheel turns. The disk brake was pre-installed.

Sounds like your rotor is rubbing the brake pads. Flip the uni over, and look through the pads of the caliper. Rotate the wheel slowly and watch how the rotor moves. When it rub the pads, just gently flex it away, keep going around and doing this until it stops. You should also check the alignment of your caliper like jtrops said. Check it using the same process as above (flip the uni, look down the caliper). It should be parallel and evenly spaced with the rotor: (d|b) as opposed to (d/b) or (d\b). If not, just loosen the bolts holding the caliper on, and move it into position. There’s plenty of YouTube videos out there to help you.

Yeah, I guess I didn’t consider the brake pads because that sound isn’t normally described as “grinding.” That’s partly why I wanted to know a bit more about the sound.

When I got my uni with a disc brake, the caliper was fairly centered, but the rotor was bent enough that I had to straighten in with a rotor truing fork. You could probably use a crescent wrench just fine, but try to avoid touching the rotor with your hands, as the oils on your hands will contaminate them. If you can tell that the caliper isn’t centered, sometimes on hydraulic brakes, you can loosen the caliper bolts, squeeze the brake lever and re-tighten the bolts while still squeezing the lever, and it should be fairly centered. I’ll also use a piece of white paper behind the caliper and the rotor and eyeball it. You have to be a little gentle while turning the bolts at first, or the caliper moves while you’re tightening them.