Try one on a music program.
Your high input levels are doing over the processing and kicking in the OLC (output limiting compression) or you’re overdriving the receiver and getting harmonic distortion which is usually about 10% at the fully driven state.
1 why do you need the sound to be this loud? (it’s damamging to your hearing and the aid)
2 get a quieter hearing aid music program with the processing turned off and the MPO set to the max.
3 don’t wear the aids in this environment - ER plugs would be better.
All of which is nothing to do with the mic.
AND I also have a Guitarist who is happy with the Unitron music program.