OK, this is just a quick rip-off of one of the smaller
trains I'm working on in my new level. Start walking
down the slope backwards (the trigger is on the slope), 
so you can see when the train
starts moving, and watch as it rotates down the hill,
then back up when it reaches the bottom. I have found
that the 'noise' key seems to work only on multiple-car
trains, as I couldn't get it to work on this single car
jobbie. 
The same principle applies for horizontal corners, only
difference being you butt the path_corners up around the
bend, as opposed to down or up the slope. I've included
the map. file so you can pull it apart.
You'll also see there is no need for a path_corner inside
the carriage to target another path_corner at the spawn
position if you build the train where it's going to spawn.

I screwed that bit up in the tutorial (sorry). If you build the train
where it starts, you just target the path_corner in the first(or single)
carriage to the next path_corner. You'll also see in my map the start
of a curve at the end...the train will quite happily go around the
curve as well as down the slope, just change the direction of the
rotation in the path_corners the train is following when the curve begins.