Transcendental Meditation creates a state of dynamic Silence.
Primordial Sound Meditation creates a state of static Silence.
The TM mantras are dynamic mantras, because they are derivations of Shakti mantras. Shakti is the principle of Movement and Vibration. Therefore you get a state of dynamic Silcence, which means that there are still prana flows going on while being in the Silent state. The Primordial Sound Meditation mantras are not Shakti mantras.
