Hi,
It's a arpeggiated sound, if that's what you mean. It play an Random arpeggio based on the notes you hold.
You can stop the arpeggio in the Advanced section under LFO/ ARP. Just deselect the PLAY button. The 4. button from the right.
The arpeggio is set to Random Mode, 3 Octaves, 2 Note Repeats in the Arpeggiator.