depends...
With an AIO, "CPU fan" is actually the water block pump and that should be running max speed ALL THE TIME. It should never be less than 100%...and that's probably around 3000rpm. You have to make an adjustment (usually in BIOS) to change the fan/pump speed to voltage controlled, 12V at all temperatures.
When adjusted like that it will vary in speed a little bit since the +12V line from the PSU also varies a little bit depending on how you're using the system. So all you're looking for is that it run 'around' 3000, with variances expected and allowed. Some monitoring utilities report the +12V line voltage if you want to see how it varies.
But if what you mean is the radiator fans then 3000rpm is way to fast, probably...