Ash I don't know if this will help. My 300D does the same thing only turning left. I found the right rear wheel bearing is slightly loose. I have not had time to repair it so I don't know that will stop the squeal. You might want to check all four wheels for slack, that could cause a brake pad to make slight contact. just my thought's.
2006 E350 98K miles
2013 Ford Explorer 15K miles