There are 2 lines of sounds under the rhythm in Sequencer 1, and Sequencer 2, where you can enter a custom sticking using the R,L,K,H buttons, or keyboard, or konnakol.
If you don't enter anything under the notes, the rhythm will play back using whatever sound is assigned to the H button. If you want a different default sound, then change the sound associated with H.
You can imagine that Line 1 and Line 2 are always filled with invisible Hs unless you've entered something else.
If the mixer faders in Line 1 and 2 are all the way up for a sequencer, you should expect to have two instances of the default sound playing back.
So, if you've entered something with the sound buttons (R,L,H,K) in Line 1, but Line 2 is empty, you'll still hear the H sound played for every note. Simply pull the Line 2 fader to zero to mute that default sound.