I sometimes do meditation repeating a non-word sound as a mantra as taught in TM (transcendental meditation). Can you suggest an alternative mantra? Since I do not know Hebrew something in Hebrew could be used for the sound value.
Mantra meditation is a form of Eastern meditation and as such it will not accomplish the goal of Jewish meditation. Mantra meditation takes a word or a sound and repeats it endlessly trying to wipe out, or cover over the normal thought pattern that a person experiences. When thoughts are fast and furious, one repeats his mantra just as fast. Then, when the mind is quieter, one repeats the mantra more quietly with the hope of stilling, or at least calming the mind.
The goal of Jewish mediation is much higher than merely calming the mind. Yes we want to calm our minds, but this is not enough. Instead of trying to merely blot out, or cover over our thoughts, we try to turn our thoughts onto holy subjects. Our goal is to use our meditation techniques to try to gain a spiritual sensitivity, an awareness that will help us attain a proper spiritual perspective.
For more detailed information see my recent video on this subject.
If you still wish to continue using a mantra then I would recommend you using the Hebrew word "Hashem." Hashem literally means, "The Name." It refers to the most holy name of G-d, a name that is too holy for us to pronounce lest we come to use it for mundane purposes. Say (or think) the word slowly and repeat it and once in a while remember that you are that you are mentally calling out to G-d. So do not just keep calling out without stopping from time to time to say something to the Holy One you are calling.