One of the first things you are going to be asked here is whether you have actually looked under the car yourself? Nobody can help diagnose over the internet without knowing any facts about your car. Get down and look at every part of your exhaust that you can see, then report back what you have found. Unless you have a great relationship and know you can trust your dealership, I would never recommend going to them with something you have not at least looked at yourself. I can only imagine what all they did cost you, unless you have no way to do any of it yourself it's too much. I am saying this from experience, before I was comfortable working on the focus I had. It's especially frustrating when your issue is still not resolved after throwing parts at it. Good luck, please report what you eventually find is the issue.
2004 Blue ZTW, 2.3 L Duratec, Stock Everything
149,000 miles, Autolite 103 Copper Gapped .051,
Fram PH3600 Oil Filter, 5-20w Full Synthetic Oil,
General Altimax RT43 tires.