Reply To: Mekor for this Rosh Hashanah Minhag

Great question! I once said torah on this as follows:

Count the syllables, including all the shva nas, in the following:

מדוע בשש רכבו לבוא מדוע אחרו פעמי מרכבותיו

= 22

Now it says in the next posuk, אף היא תשיב אמריה לה
Which Rashi explains to mean that she said to herself:

מה אני מתמהת על עיכוב בני

Count the syllables:

= 11

Altogether 22 + 11 = 33

Each one was a יללה made up of 3 קולות. So 99. Add a כולל and you have 100