I'm having problems with dark frames using my FLI 16200 microline CCD camera. The problem was present when it arrived as new. All my dark frames have two gradients across the image, one curvalinear from the top to the bottom and one horizontal across the upper third of the image. The same artifacts occur at all imaging times (30s, 300s, 600s, 1200s) with the imaging done in a dark closet, with the camera alone and covered, or with the telescope mounted. No changes occur whether the samples are obtained with SGP or the FLI grab acquisition. No light leak is present with careful high intensity flashlight shining on the camera. The gradients are difficult to remove in Pixinsight but can be done. The attached image is a jpeg of 31 stacked 1800s images processed in Pixinsight. The image is STF autostretched. Does the camera need to go back for service? Any suggestions would be appreciated. Thanks to all.