Is the muezzin's feeling of displeasure toward his unmelodious or unembellished adhan, out of fear that it will not affect listeners, considered showing off (riya')?

Improving one's voice for the adhan (call to prayer) is praiseworthy and desirable. Ibn Qudamah mentions that it is desirable for the mu'adhin (caller to prayer) to have a loud and pleasant voice, as it is more moving for the listener. This is because the Prophet (peace be upon him) chose Abu Mahdhurah and instructed Abdullah ibn Zayd to teach the adhan to Bilal due to the beauty of his voice. One should improve their voice with the intention of following the Sunnah and attracting people to prayer, while repelling the whispers of Satan regarding ostentation (showing off), and not abandoning good deeds out of fear of it.