Here's what we *do* know:
* The Tetragrammaton is YHWH. This is the four-letter Hebrew name of God, written with the consonants יהוה.
* Ancient Hebrew pronunciation was different than modern Hebrew. There are no vowels in the written form of the Tetragrammaton, so the vowels were added later to aid pronunciation. The precise vowel sounds of the ancient pronunciation are debated.
* The traditional Jewish practice is to not pronounce the Tetragrammaton. Instead, the word "Adonai" (Lord) is substituted when reading the Torah aloud. This practice arose to prevent the name from being uttered lightly or disrespectfully.
* There are theories about the pronunciation. Some scholars believe it was pronounced *Yahweh*, others *Jehovah*, or even *Yahu*. However, none of these are definitively proven.
So, to answer your question directly: we don't know the precise pronunciation of the Tetragrammaton in its oldest form. Any pronunciation you might hear is speculative.