All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.
First of all, we ask Allah to cure you.
You should know that Takbeerat-ul-Ihraam is a pillar of the prayer without which the prayer is invalid. So you should strive to resist this Waswasah (obsessive whispering) as much as is possible and say the Takbeer normally.
No matter how much the devil whispers to you that you did not say the Takbeer properly, do not pay any attention to his whispers. This is the only solution for your problem.
It is not a condition to make yourself hear the Takbeer; it is enough to move your tongue and lips with it.
If we presume that you are absolutely incapable of saying the Takbeer, then, in this case, you start your prayer with the intention, just like the one who is incapable of learning the Takbeer, because Allah does not burden a soul beyond its capacity.
Tuhfat-ul-Habeeb reads, “If one is totally unable to say the Takbeer, such as the dumb person, then he starts the prayer without saying it, as stated by Ibn Sharaf.”
However, as long as you are able to say the Takbeer, even while having Waswasah, then you must say it.
Allah knows best.