It has to do with the believed or perceived successors of Muhammed. The Shi'a believe the legitimate, (divine) successor was Ali, the fourth Caliph. Sunni believe...something else. Something about the re-establishment of the authoritative line after WWI and the dissolution of the Ottoman Empire. I don't know what...(smile), but it appears to be very serious. They are ready to kill each other over it. So, you can go figure that both are ready to kill anyone else, Christians, Jews, Buddhists, Zoroastrians, Hindus, with little concern or thought. Sort of like killing a hog.

You have Quran sent to Muhammad Peace Be Upon Him. You have Muhammads way of life exercising what the Quran has read and this has been doctrined into an hadith. Thats it. ISLAM is complete. Any addition of terms Like Sunni etc is not in realms of islam. As Islam was complete before Prophet Muhammads demise. So as an analogy. If Islam is a Glass of Pure water. And then I go to another source of water ie. river, stream, fountain and add to the Glass of Pure water. The First Glass of Water could be contaminated, impure etc. Any addition of new innovation or sects added after Prophets Demise is falsehood. So Shiahs are not from the source. ( Glass of Pure Water). It was a sect created after the PRophets death to create supremacy of the Companion Ali the Caliph over The Prophet Muhammad Peace Be Upon Him. This is an innovation, addition which created turmoil, seperation of brotherhood, wars etc. An innovation to Islam is not from Allah ie. Quran. But could be from Satan to distort and misguide. So back to your question. For Shiahs to have their own Azan is blasphemy and disrespect to Allah and his prophet. To innovate an new believe set by picking and choosing and distorting the quran, and fabricating ali a companion is a higher level than prophet is falsehood and not from islam. And the Shiahs want rights as much as Sunni muslims. Total fraud. We should reject any practise from a sect which has weakened itself with corruptive practices such as Mataa which allows you to do Nikah for 10 minutes, have sex and divorce. Basically prostitution which is forbidden in Islam. But shiahs practise it. If you want to remain true t oyour religion hold on to the rope of Allah (The Quran) and follow in the footsteps of Prophet Muhammad Peace Be upon him, as he did 1500 years. Not any practices devised after his holy demise.