It seems there could have been not one but two gunfire incidents in the area of the royal palace in Riyadh on successive nights -- Saturday April 21 and Sunday 22.
The April 21 incident is well-documented. Saudi security officials told Reuters that the gunfire lasted only about 30 seconds and brought down a recreational drone. There is amateur video footage of the incident that posted to various websites but it's not time-stamped and it's impossible to peg the location from what I've seen of the videos. See U.S. based "Right Side Broadcast Network" report at YouTube for a roundup of the videos and discussion about them.
On April 22 FARS (Iran's state news agency), reported as 'breaking news' that heavy gunfire was occuring around the royal palace and noted it could signal an attempted coup in progress. The gunfire reportedly lasted an hour. Mainstream media and official Saudi sources have not commented about this supposed second incident.
Below is the second report published on Sunday the 22nd at FARS regarding the alleged April 22 attack. The report relies heavily on claims made by an anonymous 'whistleblower.'
FARS has passed along statements from the same whistleblower several times over the past few years; it seems he -- or she -- has enough readers of his Twitter page that FARS takes him seriously enough to quote.
I haven't read enough of the FARS English-language reports on the whistleblower's claims to attempt to gauge how reliable his earlier predictions and 'inside scoops' have been.
I think the most interesting passage from the second FARS report on Sunday is the claim that while some assailants in the alleged April 22 incident were killed, several got away without a trace.
April 22, 2018 - 4.1 [I have no idea what the 4.1 timestamp translates to, ahem FARS]
TEHRAN (FNA)- Saudi whistle-blower Mujtahid, who is believed to be a member of or have a well-connected source in the royal family, underlined involvement of a number of Saudi officials in what he called a Saturday night coup against the royal dynasty.
"The attack was launched using a vehicle equipped with a 50-mm machinegun," Mujtahid wrote on his Twitter page on Sunday.
He also referred to a twitter post released by Sowt al-Arab, and claimed that Saudi Crown Prince Mohammed bin Salman has been the target of the attack, adding that 7 soldiers have been killed on both sides, while other assailants have disappeared without a trace. [emphasis mine]
Mujtahid added that a number of Saudi figures affiliated with the royal family were involved in the attack.
He also said a drone has also been used to help the assailants to find their target but the whole incident was a gunfire [gunfight?] which lasted one hour.
Heavy gunfire was heard near the Saudi King's palace in Riyadh Saudi Arabia, while King Salman was taken to a bunker at an airbase in the city.
A growing number of videos surfaced in the media showing that heavy gunfire erupted around King Salman bin Abdulaziz Al Saud's palace in the capital, Riyadh. [Pundita note: It's not clear whether these are videos taken on the 22nd or ones from the 21st.]
Reports said the king and his son, Crown Prince Mohammed bin Salman, were evacuated to a bunker at an airbase in the city that is under the protection of the US troops.
While Saudi officials and media were quiet over the incident, there were conflicting reports about the incident. Witnesses and residents of the neighborhoods near the palace said a coup was underway, while other reports said a drone had been flying over the palace.
Saudi opposition members claimed that "a senior ground force officer has led a raid on the palace to kill the king and the crown prince".
Videos also showed that a growing number of armored vehicles were deployed around the palace. 'Bin Salman's special guard' had taken charge of security in the capital. Riyadh's sky had been closed to all civil and military flights as military helicopters from 'Bin Salman's special guard' were flying over the palace.
There is yet no official report on any possible casualties.