I got Tektro HD-M275 hydraulic disc brakes with 180mm rotors, front brake is working perfectly with no issues. Under light braking rear brake works normally without any noises or vibrations, but as soon as I start to apply little more pressuer on the lever rear brake start to make grinding noises. The noise that it's making is not the same as the rotor rubbing against the pads, it's very strange. It sounds like metal rubbing against each other and during heavy braking I can feel like small vibrations through the seat. I've tried to align the brake but it doesn't seem to make any difference.
The one thing that bothers me are the brake pads, to be more specific the left brake pad. It's placed directly in line with the brake caliper itself, so maybe when I brake the right pad presses onto the rotor and pushes it to rub againts the caliper?