I think you may feel the thymus gland. Front on the thymus, it is ice cold, paralyzing. The back of the heart chakra, back extension is hot, fiery, and has proprieties of pulsation. The front of magnetism. The back is connected with the shoulders, the front with the throat, and the upper chakras by inclusion in the system.
The vibration is dual as in a car motor, the upper front part is the response of the lower back, rippling both in synchronicity. If activated at night when the vayus are felt, you can astral project or whatever you can develop from this. It has also direct relation to the aura, and you can either make yourself denser or lighter. This is more complicated but the neutral chakra is also very important, essential, and amazing in its expanded abilities.
The frequency of the vibration is the middle range, and the modulator of the whole aura in a sense, by the clash of the abrupt lower vibrations with that of the higher. It is also front and back, up and down. It does not go sideways.
The front is activated by descending flowing energy from the head or simply meditation and energy work. The back from the spine rising or Kundalini energy. The Serpent will activate 3 suns on your back, the tail, the heart and the 6th chakra before hitting the Crown.