If I've got it right, it is one of these aluminium shields that are above the exhaust that has fallen down and is touching the exhaust. If so, what has happened, normally, is that due to the interaction between the chassis - steel, and this shield - aluminium (dissimilar metals), the area of aluminium above the steel retainers has "melted/dissolved" and the shield has dropped down over the retainers. What I do when that happens is, remove the retainers - you might need to bend the tangs so that they can be reused, cut up repair washers big enough to cover the holes in the shield(s), lift shield back up, force a repair washer on followed by the retainer. Empty tin cans provide suitable material.