<p>Earth’s only active carbonatite volcano Oldoinyo Lengai, Tanzania, is a peculiar endmember of volcanism in a young rift segment. Targeted by many petrological studies due to its effusive, cold carbonatite eruptions, its subsurface structure has only been recently explored using geophysical approaches. Here we use data from a short-term seismic deployment, to exploit coherent seismic signals in the frequency domain to detect, characterize and locate volcanic tremor. We show that narrow-band tremor is related to degassing and the ascent of carbonatite melt across the crust close to the Natron border fault, which was previously linked to the ascent of carbonatites. We further show how narrow-band and quasi-harmonic tremor partly alternate and interpret this as the interplay of deeper magmatic injections into a shallow reservoir which causes resonance. Our findings yield important implications on how physical properties, structures and dynamics of volcanic plumbing systems are linked to tremor signals.</p>