Focus starts repeating the cast sound rapidly a while after starting the channel (Roughly 3-4seconds after the start?). This also happened with disintegrate, so it seems like it might happen with every single channeling spell - I have not tested others.
One thing to note though is that the SFX stopped for disintegrate after going into negatives with mana. Obviously not applicable for Focus.
Love the game so far though, just really want to use those spells but the SFX really makes it hard <3
Thanks! <3