Whether you have mechanical or hydraulic disc brakes, centering your brakes can be tricky. The brakes will almost always require adjustment when you first assemble the bike as the front wheel needs to be installed.
If attempting yourself and you still need assistance after reviewing the videos below. Please provide video of the noise, and pictures showing the alignment of your brake rotors and pads. This will help us understand the situation so we can better assist you.
Possible causes of noise:
- Disc brakes often make noise during normal operation. This can happen in certain situations like long descents, cold temps, etc. It is important to understand that noise in these circumstances is considered normal operation, cannot be reduced and does not require attention.
- Poor alignment or centering of brake calipers.
- Oil or other contaminate on brake rotors or brake pads. Even oil from your finger could contaminate it.
- Brake rotors and pads have not been bedded or broken in.
- Brake pads or brake rotors became hot from heavy braking and glazed over.
- Loose brake rotor
- Loose brake caliper
- Loose brake pads
This article gives a very good over view of the pros and cons of different brake pad materials: https://www.merlincycles.com/blog/buyers-guide-to-disc-brake-pads/
Metallic brake pads last longer, withstand heat better, but can be noisy. They also take longer to bed in properly.
Organic brake pads are typically quieter, have great initial bite, but do not withstand heat as well, and do not last as long in general.
This is a process that a bike mechanic will be able to preform best, but if you want to learn to maintain your bike yourself throughout the lifetime of your ownership, there are some very helpful tutorial videos available for adjusting disc brakes and removing the screeching or squealing noises that can often come with having disc brakes.
Here is some very helpful 3rd party information:
Article with pictures: How to stop squeaking disc brakes
1st Video: As the title suggests explains "A Quick Adjustment"
2nd Video: Discusses noises, cleaning your brake rotors and pads, sanding your brake rotor or even filing your brake pads if they became hot during heavy braking and are glazed over.