2003 Toyota Celica problem?

Whenever I brake I hear a sound coming from back brakes similiar to the sound when a bed bounces or squels. I took it to Monroe Muffler a few months ago and the mechanic said it had something to do with the emergency brake and dust and to just place the emergency brake up once a week to get rid of the bouncing noise whenever I park. I do this but the noise is still present. Is anything else wrong?|||check for adj. on all brakes...something is loose