blown muffler?

From looking at a muffler how can you tell if its blown? I just found a spare banks monster muffler at my moms house that I forgot I had and am thinking about swapping it on now that I have headers. I picked it up and it sounded like some of the packing was freely moving in the shifting side to side. Is that normal for a broken in muffler? I was always wondering if this muffler was blown or not when I had it on before cause it was never as loud as all the other banks I have heard.