most probable scenario-- increase the attack time (slider) ever so slightly on the synth to create a short fade in on the sound.
if you’re using someone’s preset, chances are they may have programmed a very quick pitch envelope at the beginning of the sound using a mod envelope; if that’s the case, disengage the modulation assignment to pitch.
less likely…
if you’ve bounced to audio and it still clicks, chances are you’re compressing it with too short an attack on a compressor, and it’s acting on the individual cycles of the waveform and creates clicks (lengten attack time on compressor).
or there are zero-crossings issues. fades or nudging the waveform helps.