Either a pistol or a mantis shrimp. The majority of pistol shrimp are fish/reef safe. Mantis, however, will prey on both invertebrates and fish. Try using a flash light after lights out, when you hear the noises, to see if you can identify the source. FWIW with 85 lbs. of LR
it would really surprise me if you did not have either a pistol or Mantis hitchhiker, if not both.