In the Biblical Hebrew of antiquity (before 400 BC), the word was probably pronounced approximately /jahwe/.
A preferred pronunciation based on evidenced from Biblical and Non-Biblical sources is (Yah-hoo-wah)
Many scholars believe that the Tetragrammaton, or four-letter name (YHWH), should be pronounced as YAHWEH (yah-way). Some others have settled on Yehovah or Yehowah due to the vowel pointing of the name by the Masoretes. The vowel pointing of the Tetragrammaton unhappily was done in the strict rabbinic tradition of not speaking His name aloud. Therefore, the vowel points of the title "adonay" were inserted in YHWH to remind the reader to say that word aloud (which means master or sovereign) instead of the true name of the Creator. This was a deliberate disguise by the Masoretes of the Creator’s name that was carried over into the names containing parts of His name also, such as those beginning with "Yah-" and "Yahu-." Later on, the translators, who apparently were not aware of the rabbinic restriction and the disguise placed by the Masoretes, transliterated the name Yahuwah with the installed vowel points, and arrived at Yehovah or Yehowah. After the arrival of the letter "J" in the English language, prior to 1633 the Y was modified to J and became "Jehovah." All of these renderings were incorrect for obvious reasons and not the correct name of the Creator. The first English language book to make a clear distinction between 'i' and 'j' was published in 1633.
Some of the personal names containing "Yah-" or "Yahu-" were not modified by the Masoretes and those few names help point the way to the real name of the Creator. Also, an acceptable abbreviation of His name is found in scripture and it is a valuable clue to the correct pronunciation also. That abbreviation is YAHH (with vowel pointing) and shows that the first two syllables of His name could be pronounced in that manner.
Non-scriptural evidence also bears proof to the way the Creator's name should be pronounced. In Islamic written tradition since the time of Muhammad, written evidence shows that the name of the "Jewish God" sounded very much like "YAHU." from the Dictionary of Islam, page 227, Thomas Patrick Hughes, 1886 - ISBN 0-935782-70-2