My newly built system with an 2500k in it has got me worried. I'm sure this isn't that big of an issue. When I press the power button on my system all the fans start up like a fan usually does, except my i5 2500k that is currently mounted with a stock fan. It looks like it tries to spin once but then stops and goes back a little, then again, and goes back a little, and by now MAYBE 5 seconds have gone by at most (Why I don't think it could be that big of a deal) and then it starts spinning up really loud and fast for a couple seconds then lowers back too the 2070rpm area.
I have not touched any of the OCing software on the ASRock Z77 Extreme4 or on the chip, i have default bios currently and all my temps on my cpu cores idle at around 30 Celsius in my room.
I have an older Core2Duo proccesor and the intel stock fan does the same exact thing at every boot. That machine has been running beautifully for the past 4 years. As abekl said, if it resumes normal spinning, you will be fine.