Music on a massive scale. Sun Miners and other clades living in an environment with strong and variable magnetic fields might build the equivalent of theremins. These can reach enormous scales...
Other examples may be:
1) An asteroid belt
2) A planetary ring system ("The Jupiter Symphony" (whimsically named after an Old Earth symphony))
3) A passive theremin (similar to lidar, EM receivers) in the approach lane to a major wormhole cluster