The twin 35mm guns on these vehicles fire at a combined 1091 rpm, according to the config. However the sound does not reflect this, I recorded it in Audacity, and the sound was played at about 470 rounds per minute.
Now, they are twin guns, so the sound could occur at exactly the same time, making rate of fire "sound" lower.
However, from videos online, the guns are not perfectly synchronized, so it can sound fairly slow, but it also frequently sounds much, much faster.
The fact the rate of fire "sounds" so slow for these two vehicles makes them seem very underwhelming.
I included links to two videos below showing videos of anti-air vehicles which use the exact same twin 35mm Oerlikon cannons.