My kingston card in my K-30 has a whole different problem.
Recording a movie in a completely silent room, holding the camera steady, all sorts of assists turned off ... and i get a thump into the hd video audio channel, about every 2 seconds, with a very precise interval. At first i was suspecting that it's the stabilization, but it isn't, it's exactly in sync with writes to the sd card. On every write to the card (video buffer flushing i guess), some electronic noise is being generated in synchronization with the light emitted from writing to the card (in the lower right part of the camera's back), and that electronic noise makes it to the microphone and gets recorded in the movie. Doesn't really annoy you in noisy videos, but is pretty awkward in silent background shots.
Anyone on kingston class 10 card owners, can you confirm that ? (you need a pretty quiet environment to reproduce). And anybody who has moved to Sandisk - can you confirm that you get the same result or are your videos really completely silent ?
The card i'm using is 16GB Kingston ultimate 100x (class 10) like on this link
SD/SDHC/SDXC Flash Cards | Kingston (the blue watery one) ...