I changed New rotor & break pad causing left side wheels noisy and heating. What might be the cause and is it ok after driving 20 to 30 miles? or is it dangerous?

 

Did you change both sides? Did you lubricate the caliper sliding pins with new high temp grease? I'm assuming you were able to compress the caliper piston in order to fit the new brakes on there.Take the caliper off and verify that the outer bracket slides smoothly on the slider pins. As for the noise, it's also possible that the brake pad hardware is touching the rotor or that the heat shield is bent and touching the rotor.