Why is my bike braking so loudly?

Sounds like sound effect in a movie of some old iron gate 😂

I don’t have any useful advice but I’m following for info.

Brakes squeal like this when they are contaminated with the usual suspects being grease or oil that has gotten sprayed up onto them when you’ve been riding or transferred onto them when washing/servicing your bike.

So don’t add any extra grease (like someone has suggested) because it will not only make them noisier it can also affect your brakes performance and ruin your pads.

Get some brake cleaner and use that. The best way to do it is:

Take your rotor off and your pads out the calliper.

Spray the pads and rotor with the brake cleaner then wash them is warm soapy water.

Repeat this 2-3 times finishing with a spray of brake cleaner.

Give the inside of the calliper a spray of brake cleaner.

Leave to air off then put it all back together.

You will have cleaned off the pad residue from the rotor so they will feel underpowered so don’t feel alarmed at this, it’s normal. All you have to do is bed them in again and they should be quiet and as powerful as before.

But to be honest I’ve had mixed results cleaning pads and have found sometimes the only way to get rid of the squeal is to replace the pads with new ones. Just don’t forget to clean the rotor before doing this other wise you’ll just contaminate the new ones too.

just throw a bunch of dirt on them and call it good

Clean with brake cleaner (rotor and pad) and then brake every brake very hard like from 30km/h to 0 three times.

There is probably some contamination on the pad.
If nothing helped i sometimes removed the pad and very light sand the pads and then again firmly brake again.