Thanks for joining the processor community.
I understand you would like to know the maximum stock fan RPM's.
The fan speed is between 800-2500 rpm's. You can actually control the speed at BIOS level; this is possible if your computer bios allow changing fan speed settings.
BIOS update may help with noise of the fan, but if the fan is out of balance, this will be a hardware problem and you could contact Intel for possible warranty options
Is there any official info where i can confirm that the maximum is 2500 RPM?
I regret to inform you that this information is not available on our web site because this type of specifications is handled by the fan manufacturer. It could be Sanyo Denki, Fujikura ,Delta or Nidec Corp.
Here is an example for Delta web site: