It is the sync parameter which causes the crackling !
Asch, maybe you can test something:
1) go to preset 0012 - annoying arp
2) fx2 = delay
3) dry/wet balance is locked (black colored with no control)
4) sync = ON, link = OFF, pingpong = ON
5) play middle C on keyboard and listen: The sound is crackling
6) turn off sync (sync = OFF) and the sound does not crackle anymore
Is it ?
Thanks a lot my friend