Hi. Does this happen during playback, or when not playing?
Does it happen with all synths and fx? If not, which synths and fx is doing it?
Which Audio Interface / sound card do you use?
Which driver mode do you use? (Preferences (P), Audio, Playback and Recording)
Which buffer size do you use? (Preferences, Audio, Driver Settings)
What is your "Prepare using ... ms Buffer" in Preferences, MIDI, Playback and Recording?
If set to 250, try to change it to 500.
All the best.