Elite Brain Harvester Zombie

On that note, what I think would sound even more appealling is something like:
- Main loop has a rhythm of 4/4 (or 16/16, 64/64 -- you get the idea)
     (so there can be e.g. 64 events per beat, so 256 for the whole loop)
- Weapon procs at some X/256 event(s) of the loop on level one.
- Each speed upgrade changes the event(s) in which the proc occurs
      e.g.: procs for pistol (one time per beat on lvl 1, so four times per loop):
         - lvl 1: 32/256, 96/256, 160/256, 224/256
         - lvl 2: 32, 96, 128, 160, 224
         - lvl 3: 32, 96, 128, 160, 192, 224

That way you could control the sound the player hears even further, and maybe ensure that even the higher/highest weapon levels drum along well with the beat.