What does "vibrate" a mantra mean?

[Mulberry]

It means using your voice to sing the chant in a certain way, same as shamans use drums, to create vibrations of a certain wavelength and help induce brainwaves of the right frequency for the right level of trance desired.

There’s a good explanation here: (note: TETA means “THETA”, that’s a typo).

Vibrations and Mantras

You can hear examples on youtube to get the idea.

Vibrating mantras

Excerpt from the NAOS: Vibration: Vibration implies that each part of the word to be used, (either alone or as part of a text or key) is resonated deeply and this requires the person to be standing and the ‘solar plexus’ to be used to generate the deep breathing required, the mouth acting as a resonant cavity. The vibration should be such that it is felt in the whole body - a vibration is not a shout or scream but rather a prolonged concentration of sound energy. For example, to vibrate the …