The fan on the video card is dull, because of what?

Question

Video cards

video gtx 550 ti
4-pin fan, in idle usually 840 rpm, now it by itself raised the speed as when starting the computer 1600 rpm immediately not as usual gradually, the temperature of the video did not rise, after 2 minutes it became normal

Answer 1

I would venture to guess that the RPM sensor is clogged with dust.
looks different but is usually located under the fan impeller
how to get to it is written here cxem.net/master/53.php