For the last few days my GPU idle temperature has been 5 degrees hotter than before. The PC also kicks the fans in a lot sooner than I'd expect when gaming. Is there anything which might be responsible for that aside from a cooling fan problem? Ambient temperature can be ruled out; it's gone quite cold here and I don't have the heating on much. All fans are reported as working at their normal speeds.

Yes I know open the case and check the fans are spinning, I'm trying all alternatives first as this case is a real evil beggar to open and close. If I do open it up I want to check every single possibility at once.