Why do Iran and Saudi Arabia hate each other?

Ever since historical records began the middle east has been controlled by two ethnic groups the Arabs and Persians both with there own different languages but extremely similar cultures.
These two ethnic groups have always held a bitter rivalry trying to differ themselves from one another,  doing things opposite to each other, trying to gain an edge. an example of this would be
historically Arabs would only recognise two types of people Arabi (Arab) and Ajami (the rest of human kind) not singling out Persians as gesture to show that they are not worth even recognising.
but one similarity has always to gain influence and control over the middle east.

Before even the advent of Islam in the middle east religion was a differing factor between the Arabs and Persians. Christianity Judaism and forms of idol worshipping was prevalent amongst Arabs while Zoroastrianism, Buddhism and fire worshipping being prevalent amongst Persians.
As Islam conquered the middle east the split in Islam into Sunni and Shiite became a differing factor
between Arabs and Persians with Arabs becoming Sunnis and Persians Shia.

The differences in opinion regarding religion further fuelled there enmity. but it wasn't until the 20th  century that this rivalry would effect the rest of the world and have some serious implications.
With the Iranian revolution occurring transforming Iran from a quiet a secular state lead by a western sympathiser the Shah Mohammed Reza Pahalvi into a hard line Islamic republic of Iran being lead by ayatollah Khomeini.
And over in Arabia ibn saud with the help from the British taking control from the Turkish ottomans and implementing his extremely fundamental version of Islam 'wahabism' and naming the country after himself 'Saudi Arabia' religion was put at the forefront of the conflict.

According to the new found ideology 'wahabism' the shia were non believers therefore not Muslim. Also the  Saudis had a liking towards the Americans and a mutual friendship whilst the Iranians had overthrown an american sympathiser and didn't like the idea of being influenced by the west.
with Iran also supporting the Palestinian cause against Israel an all weather ally of the U.S relations between Iran and america became even more strained.
With news of Iran's uranium enriching program and also that Iran could be able of making the atomic bomb sanctions were imposed and relations all but severed.

This enmity has created many nail biting and somewhat frightening situations which in turn have had major consequences. when provoked by Arabia or its ally's, Iran has threatened to close the strait of Hormuz through which 20 percent of the worlds oil supply is transported which if materialised has the ability to cause havoc in the the global oil markets. Saudi Arabia on the other hand with Americas help threatens to increase sanctions further weakening relations.

This rivalry has forced many Muslim majority country's to choose a side between the two
the UAE, Bahrain and Egypt siding with Saudi and Qatar, Syria and Palestine siding with Iran just to mention a few.

Both sides accuse one another of supporting terrorism resulting in numerous proxy wars. taking in to account the Syrian example where at the start of the Arab spring the Syrian government was being supported by Iran so the Americans and Saudis thought it was a good idea to support and train guerrilla fighters and the anti establishment pockets to topple the Iranian backed Assad, providing them with hundreds of millions of dollars worth of weapons and ammunition just to fall in to the hands of what we would all call i.s.i.s.

Anyhow personally and probably anyone else that you may ask couldn't see this situation easing. unless  Saudi become less fond of america and Iran become Sunni either situations being extremely unlikely.

Thanks for reading