I had the same problem recently and it was my Hub Bearing assembly. When I would take a long curve that would shift my weight to the left the sound would go away. The bad side was the passenger in my case not the drivers in yours. I was surprised how easy it was to fix once you have located all the parts you will need (If this is your problem). You will need the Wheel bearing hub=about $60.00, the hub screw and cap about $10.00 each, and about 45 min of your time. I would be more than happy to talk you through this proses if needed. I am no expert, but I have done this and did it correctly. The cool thing is that in most other cars you would have to pack all the bearings and all that crap and put the whole assembly together yourself, but Ford made ours all put together in one neat Hub Bearing package. It could just be that you need new brakes and or roaters. All I know is th guys on this site helped me out big time and they figured out the problem for me all I had to do was fix it. Much props

What does it sound like from a stop to around 40MPH?