2005 Mazda 6 brake noise

I have a 2005 Mazda with 56,000 miles. When I press on the brake pedal it makes a crunching noise like rubber on rubber sound. The rear brakes pads were recently replaced and the rotors were turned. This did not eliminate the noise. Any suggestions? The brake mechanic at Mazda dealership told me to replace the brake fluid to get rid of the noise at a cost of $180.00. Is this a good solution and can I do this maintenance myself successfully or should the dealer do it for safety? reasons.