In fall 2014 and spring 2015, passive acoustic data were collected via autonomous gliders east of Guam in an area that included the Mariana Trench Marine National Monument. A short (2-4 s), complex, unknown sound was recorded. The call began with a brief 0.4 s long tone centered at 60 Hz, followed by a 2 s low-frequency moan that sweep from 44—30Hz. The moan appeared to have both amplitude modulation and strong harmonics. The moan was followed by two ~60-150 Hz upsweeps lasting 0.5s that often had diffuse energy up to 1000 Hz. The call ended with metallic-sounding upsweeps with most energy between 700 and 800 Hz, but up to 7.5 kHz. These sounds were recorded regularly during both fall (326 calls during 38 glider dives) and spring (110 calls during 16 glider dives). Many components were not visible in low signal to noise ratio calls. Calls were typically 5-6 minutes apart and often occurred in long sequences. Aurally, the sound is quite unusual and most resembles the minke whale “Star Wars” call. We propose this sound is biological and is likely produced by a baleen whale.