We produce sound on our exhaled breath. To soothe your nervous system, try saying ahhhh aloud extending the sound without making yourself feel breathless.
Try saying your ahhhhs in the tone of the harmonic scale ( do re me fa so la te do) Gradually increase your volume.
( do, do do) to exaggerate your ability to feel the vibration. The vibration will change as you move along the scale and with volume. After achieving peak volume, you can gradually diminish it until you are toning silent ahhhs.
Those who may be familiar with OM as the universal sound can take the ahhh sound and couple it with OOO and UUUMM and chant OM along the harmonic scale.
Since the body is largely made of water, the vibration travels pleasantly throughout the body