Anomalously high ambient acoustic noise was observed within the caldera of Axial Seamount, located on the Juan de Fuca Ridge at 46¿N. Noise spectra from 2 to 30 Hz were calculated from hydrophone signals from four separate seismic recording systems. Noise levels varied up to 25 dB over 6 km. This observation suggests the noise source is at or near the sea floor. By assuming spherical spreading, we estimate the source of the noise to be within 400 m of one of the instruments. A low temperature hydrothermal vent field, located within 600 m of this instrument, has been previously mapped with submersibles and is likely the source of the anomalous noise. A high temperature, black smoker, vent field, also located within the caldera, shows no evidence of anomalous acoustic noise.