You don't even need the hum. Just focus on listening down the middle. If you want to listen to one side or the other do so. Quit being anxious about having something to listen to. Set your purpose and let the non-conscious mind do the listening.
Check the Technique Overview that comes with each Paraliminal for ideas what you might want to think about. A mantra is good and so is daydreaming. Just let it be what it is. No need to try to do anything once you've decided what your purpose for listening is.
Alex
