I've been doing a bit of research on this. It looks like the transmission valve body (mechatronic unit) is on its way out. It's a common fault on the older Audi/VW tiptronic and multitronic gearboxes. Apparently Audi in America have extended the warranty on this part to 100,000 miles as it's a known issue, but no such cover here. Do a google search for 'valve body fsi automatic jerk' and you'll see dozens of websites about the problem. If it is this, it's a four figure sum to fix.