If it is controllable, it will be in the BIOS, probably under power settings and probably called speed fan or Q-fan or similar- it'll be an on/off option.
The burst of fan noise you hear on the hp, is the fan being fully powered before the BIOS directs the system to cut the power as it reads the system temperature data. My home box does the same.
Not all BIOS'es have it, you may find you're plain out of luck.
Edit: I've just looked in my BIOS for you & it lives in Power optios>Hardware monitor and it's called Q fan and is either enabled or disabled.
