But what is it? Just curious...

So I finally got Nissan to take a look at it since I bought it there a couple weeks ago and it looks like it was the exhaust hitting the crossmember. They obviously wouldn't dare touch the "structure" of the car so I will have to take it somewhere else or get ambitious myself. Thanks for all the responses. Anyone know what size washers or how many to use? Also, while I was under the car, I noticed I have HFC's. Can someone help me determine what kind they are?