The long yellow arrow at the top of the pic points to a crossmember welded between the exhaust pipes just ahead of the mufflers. It appears to be an adjustable movement damper.

Mine rusted through and broke, causing a loud clatter as the left 2/3rds vibrated against the right. Bending the left side up, so that portion of the crossmember no longer contacts the right, silenced it. However, I still suffer some occasionally heavy vibration, which I described some months ago in this thread:

http://www.peachparts.com/shopforum/tech-help/413163-e350-m272-engine-vibration.html#post4199790

Re-connecting the pipes should stop the heavy vibration. Before going to a welder, is there a clamp-on type of solution?

Attached Thumbnails

 

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2008 E350 4matic / Black/Anthracite

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Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black