i think he,s talking about his 7800 gtx with a custom fan =)
IF u have your old cpu cooler back and its the same as before only turned around... it shouldnt or cant run faster since the voltage didnt change unless u have a rpm controller on there or am i wrong?
check your videocard driver settings if the "Fan Always On" is enabled in the overclocking part if u got that IF its the GFX Card
If your motherboard has a temperature control sensor for the CPU Fan and the cpu cooling block is full of dust : Heat+Cpu=High RPM Fan
Hope i helped you!