You have an axle seal leak. It is a huge problem with AWD Edges - I know - I have an 08 with this problem. Go to Fordedgeforum.com and look there. A lot of people have the problem and it is re-occuring - I myself will be bringing the Edge in for the 3rd time on Wed. I only bought it at the end of December. Sometimes replacing the PTU will help, but that didn't on mine. Check out that site and hope your dealer will be able to fix it. My dealer has also seen the exact problem with AWD Taurus - same powertrain. Sorry to be the bearer of bad news, but I'd bet money on the axle seal leaking at the PTU.