So, I did wind up having Walter's fix my car, costing about $150. I wrote in to Midas on their customer feedback and got phone call response within 3 hours. A regional supervisor wanted to have a look at my car, and so I brought it in the next day. After looking at it, and a bit of negotiation, Midas gave me a brand new exhaust system. My car runs wonderfully now. And while I wouldn't recommend them nor will I go to them again, I feel a bit better about them as a company standing by their service. I'm glad this has been resolved.