It depends a lot on the bun, the kind of music that you play and the instruments. The only way you can know is by observing your buns while you play a bit. Rabbits aren’t fond of sudden new noises, so it’s probably best to go slow. It helps to build a positive association: reward them with treats or some pettings while you strike a couple of notes, they can get a bit of time to adjust to it and will learn to associate it with something good.
I listen to a wide variety of music, which also includes folk metal. This is a very upbeat metal genre which uses folk instruments like violins and flutes. I’ve never seen Breintje respond to it in a negative way, not even on the high notes. What he does hate is the neighbour’s dance music with loud bass thumps (these make the floor vibrate). It makes him very nervous, but I guess that’s logical because rabbits signal danger by thumping their feet. His instincts must be going wild then