Civ4 BTS (Steam) "mini-freezing", Windows 7

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Doing any in-game action (like toggling resource icons, selecting or moving a unit...) or closing the graphics page in the options causes a freeze that lasts up to around 10 seconds. This wasn't happening before on this PC, and other games perform just fine.

 

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The combination or one of the two, restarting my computer and playing in windowed mode, fixed the issue for now.