Two mufflers on 89 Supra ?

Soon hopefully, I will have an owners manual for my Supra. While looking at the underside of my Supra I saw what looked like a small muffler; it was between the cat converter and the muffler/tailpipe assembly. I looked for this in the Haynes repair manual and it's not even in there. Does anyone here know anything about it ?

It may be a resonance chamber to cut down on noise.