Incorrect drum sounds
S4 - Minor
The drumset play back uses the sound of a timpani along with the drums. Some of them are quieter than others. I've tried changing the playback sound to different sets of drums but they all do the same thing.
In order to understand your issue and assist, we would need you to attach your score and tell us what soundfont you are using. Most likely there is simply some mismatch between your drumset definition(s) and the soundfont you are using, as in general, drumsets sing the default settings and soundfonts work just fine.