I have had a similar problem on my Note 3 which I haven't rectified yet as I haven't bothered to order a new card.
Just wondered if you get a fizzy noise or feel as you insert the card, as if there is a tiny strand of copper wire folded inside.
I started losing battery performance and kept getting a notification that 'sd card unexpectedly removed', quickly followed by 'Preparing sd card'.
It forced me to do a 1st factory / master reset and I have left the card out for 2 weeks now and getting great battery life. I put it back in straight after the reset but it recurred.
However the card data (ripped music, photos, docs, apps) is all intact via my pc. Then I tried a spare 2gb card on the Note 3 temporarily and it worked with no notifications.
Anyway, still curious about that fizzy noise and feel.