By default, Sonar will automatically enable the input echo on functionality, as you select a given midi track.
When you select a different midi track, Sonar will disable the first midi track's input echo on, and will then turn it on for the newly-selected midi track. Please note that if you had manually turned input echo on for any midi track that Sonar will then NOT automatically turn it off for that track. (you would have to manually turn it off for any such midi track where you had manually enabled input echo on).
If you are hearing multiple midi tracks playing, it is most likely that you have multiple input echo on buttons lit. Try either manually turning the undesired ones off by clicking on each input echo on button so that it is not lit, or just click with your mouse to select the track that you actually want to hear the midi for, and Sonar will as I stated earlier turn off the input echo on for the non-selected tracks and will end up with input echo on for only the track you just selected. Again, Sonar will not auto disable input echo on for any midi track that you had manually enabled it.
Sorry for any confusion generated by my woeful explanation above. I have some pretty good pain meds going and have not had any coffee yet.
Bob Bone