Was the tunnel to add to the ride experience or was it more to squash those pesty noise complaints? 

What a great addition.  It's a HUGE shame Clementon didn't do something like this!

I think the hill going into the tunnel is one of the best airtime moments of the ride.

It's good too! I don't remember it being ridiculous. The crazy moments that stand out in my memory are:
1) the first drop (front seat). You get catapulted over the top due to the little rise before the drop.
2) the little hop after the first drop (front seat). Scary airtime, especially if the restraint doesn't cover all of your lap!
3) the entrance of the tunnel (front and back seat). Awesome airtime and headchopper!
4) the final hop before the turn into the brakes (back seat). If I recall you get a violent jolt of airtime in the back seat and a much gentler pop in the front seat.

Overall there is plenty of airtime anywhere on the train. I'd say it's about a 50/50 split between the front and back seat, where as I prefer the back seat on most other woodies.