Loud rattling sound from front right (wheel?), especially at low speed

What is your question?

I hear a constant loud rattling noise which seems to be coming from the right front (wheel?) of my 2001 Chevy Impala. It sounds like loose metal clanking on metal, especially at lower speeds. On the highway it's not as loud, although I assume this is due to highway noise. The recurring answer to the question of what could it be from those friends have heard the noise, is the car has a broken cv joint/axel. I took it car to my mechanic who diagnosed it as a parking/emergency brake issue. I could find nothing online connecting any noise resembling what I've described with brake problems. I've used this same mechanic for over 10 years. He has an excellent reputation and I normally trust his assessment. But the similar opinions of others creates doubt. Any information would be appreciated. Thank You, Jennifer