I only have this happen if I fill the buffer, yours sounds like it takes much longer then mine. How fast is your card? Are you sure it is not a reliables knock off card, doubtful it would be if bought at a good store but from some online places anything is possible if they aren't well known vendors. I have noise reduction on mine on as well. How many shots do you fire off in a row. In Raw if you are doing a lot of rapid fire it can fill the buffer quickly.