Mystical sounds:

As one advances in meditation, mystical sounds are often heard, such as those of the bell, conch, flute etc. These sounds are a precursor to the deep silence.

Lights:

In the beginning, spots of various colours may appear. As one proceeds, tiny balls of white light may appear which may become quite big. The appearance of light implies that one is transcending physical conciousness. Do not disturb the body and breathe shallow. One may even start seeing forms.

Detachment:

As one proceeds through meditation, a great tranquility is experienced wherein the sensual objects would not have an attraction. A feeling of being desireless and fearless is experienced. Eventually the meditator may even feel a separation from the body.