What is the music in Naruto Shippuden episode 156, "Surpassing the Masters", at the 4 minute mark? I've also heard it at the end of episode 151. It has a bit of banjo and violin.
This is an unreleased track. I found a version of it on YouTube titled "Peaceful", but it's incomplete and has sound effects in it. There might be other versions online, but I didn't find any others in a cursory search.
(To make things more confusing, there are at least a couple of other unreleased tracks that have been given names like "Peaceful" and "Peace" and "Peaceful theme" too...)