V.T.N.: While doing japa of AUM, does it mean that I should become one with that sound by its constant repetition ?

Babaji: When you meditate on AUM or repeat AUM mentally, you should entertain the bhava or feeling: 'I am the all-pervading, pure, satchitananda atma.' You need not be one with the sound. What is wanted is feeling with the meaning I am Brahman.