When you fold the seats flat, you'll see a metal peg which allows latch to allow the seats to 'clip on' in an upright position. I just put wrapped layers of duct tape around the latch, and the issue is resolved.

 

Haha funny I found this thread, just bought my A4 Avant on Friday, drove it home to Fort Mac and and the next day had all kinds of squeaks, figured it was just the cold leather, we hit -32* that night. Will have a look over these seat latches. I thought it was my spare wheel rubbing so I took it out and put it back in and tightened it down nice and good.