I just got a new bike with the magura MTS brakes on it, but when the brakes are wet they make a really loud squealing noise! This is the first time i have ever heard any brakes squeal this loud. How can i make them go quiet?
Take the bike to your shop and get them to throw away the old pads and order you some new Jagwire replacement pads. And make sure you ask them to show you how to bed in the pads properly.
I would first clean the rotors by taking them off and using brake cleaner(i use automotive brake cleaner). Spray them down, wait about 45 seconds and wipe of and excess of( you want to leave a film of it), then carefully put them back on and make sure you dont touch the braking surface and Then spin the wheels and use the brakes a couple times. Then on you next ride see if they are more quiet. If that doesnt help new pads and some times new rotors can help.