I recall seeing this kind of problem before (but have not experienced it myself). The cause seems to be that the default setting in BIOS for the low fan speed warning trigger is set too high - like maybe 700 rpm in your case and your fan does not need to run that fast at start-up. There is a place to manually change this trigger point for the fan low speed alarm in the BIOS area where you configure that fan's control system and see its speed and the CPU temp.
Before doing this, check the specs for the proper operating temp of your CPU, versus what the BIOS reports is the real measured temp. Is your CPU actually running very warm even under no load at start-up? If it is, then do NOT change the fan alarm. Check out why the temp is high, and why the fan is slow. Maybe you need to re-configure the fan automatic speed control system.