Halion Sonic 3 expression map for Studio Strings?

Hi all! I’m creating an expression map to use with Halion Sonic 3 Studio Strings, using Cubase Pro 9.5. I have partially succeeded… I have one instance of Halion, with different articulations loaded on channels 1-6. I now have articulation lanes visible in the lower window of the instrument track, which I can use to indicate which MIDI channel / articulation to use for each note. The trigger notes are assigned to the lowest octave available, below the playable range of the instrument.

This setup is successfully switching between articulations, but is also generating sub-bass noise from the trigger notes somehow. I’ve tried changing the low range of the instrument in the expression map setup so it is higher than the trigger notes, and checked to be sure the trigger notes haven’t been duplicated in the instrument track. Unintended noise is still present. I’m an experienced Cubase user, but completely new to expression maps. Any ideas what’s going on?

Thanks in advance for any suggestions!