Exhaust / Muffler question

[VXD959]

Trying not to hijack Vinnybin's , and using the pictures posted there by JAMAS...My VX started to sound very loud over the weekend. I checked under the VX today, and the issue seems to be the section highlighted in the picture.

Question:
What is that section?
Can I just replace that section?
Should I replace the whole muffler?

Thanks in advance for your advice.