During meditation sometimes seekers hear the sound of Aum, although they have not said it out loud and nobody in the room has chanted it out loud. This means that inwardly somebody has chanted Aum or is chanting it, and the meditation room has preserved the sound.
Chanting a mantra can be done while you are driving or walking along the street or standing in a public place. If you silently chant while walking along the street, you are not withdrawing; only you are trying to protect yourself from the unaspiring world. You are increasing your inner strength and inner capacity. Then, when you are inwardly strong, you will no longer have to chant; you can just move around and not be disturbed.
Any method of spiritual discipline will have two inevitable and inseparable wings: absolute patience and firm resolution.
If you are trying to maintain a high consciousness when you are in a public place, it may be difficult for you to go deep within and bring peace to the fore. But even when you are surrounded by the noise and bustle of the outer world, you can easily bring forward a louder sound. This louder sound is not a destructive sound but one that contains indomitable power. It gives you a feeling of how potentially great and divine you are. If you can bring to the fore the divine inner sound, which comes from your heart, or if you can enter into that inner sound, then you will see that the outer noise of the world is no match for it. To your surprise, you will see that the sounds which disturbed you one minute ago will not bother you anymore. On the contrary, you will get a sense of achievement because instead of hearing noise you will hear divine music that is produced by your inner being.