In the Arab world they consider it wrong to sing/hum any tunes that have the names of Allah or when u give salams to our Prophet pbuh. There are different versions of the Darud that shud be recited as many times as one wants, but it shudn't be sung that's the only objection people have here..
Same thing with naats, people sing it to tunes (at times even bollywood songs) and that is considered wrong.. the only way to praise Allah swt is mentioned in the Quran.