My question is concerning the ghunnah: Is it a must to keep the sound of the ghunnah steady , not going down or up?

Question
Assalamu alaikum wa rahmatullahi wa barakaatuh,

May Allah reward you for your efforts and make us all among his thankful slaves.

My question is concerning the ghunnah:

Is it a must to keep the sound of the ghunnah steady , not going down or up? Or is it only not allowed to raise or lower the sound like a ladder (like during the mudood).
I am confused about this because I heard it in the lesson (on Iqra) of Shaikh Ayman Suwayd ,but I don't really see anyone practicing this.
Thank you very much. May Allah help us to give His book it's rights.  And may you be helped by Asshakuur as you helped others.

Answer
Wa alaikum assalaam wa rahmatullahi wa barakaatuh.
Subhan Allah, the wording in your question is indeed beautiful, may Allah be pleased with you and reward you greatly for you good adab and grant you all which is khair for you in this world and the Hereafter.

We should not oscillate our voice or tone during the prolonged ghunnah, such as when the noon or meem have a shaddah on them.  This is not the way the early Muslims pronounced the ghunnah and is a modern way some use to try and beautify their recitation. 
We should beautify our recitation with a pleasant voice, apply the proper tajweed rules, and concentrate on the meaning of the aayaat and try and convey the meaning in our recitation without exceeding the proper rules. This is the best way of recitation. 
May Allah grant us that we recite His words as they were revealed to our Messenger, peace and blessings of Allah upon him and that we do not surpass the bounds of what is proper recitation in our efforts to make it beautiful.  Ameen.
You are most welcome and may Allah reward you for your kind dua'.