Yea looks like a coolant line, to the heater matrix perhaps?
Should be easy enough to change, just be careful as it looks like it connects to a plastic T-piece while will snap if you put too much stress on it.
So in gears 1&2 there's no problems?
3rd gear at 1900 it's shaking like mad?
4th-6th what happens?
Driving on the motorway at 70mph, knock it out of gear and coast in neutral and it's rattle free right?
Might be looking at a gearbox replacement
It's not terrible, you'd need to check the service schedule to see if anything big has been missed, but the dealer has done a decent job.
You need to check if the cam follower has been checked and/or changed as part of the work they've done.