I currently own two lenses - 35mm and 18-200mm. I notice that on my 18-200mm, any shot I take at a focal length of 95mm and above will have a small speck in the top of the image. Is this due to my sensor or the lens? Any suggestions how to get it removed? (if I'm taking it to cleaned, am I asking them to clean my sensor or the lens?). The body is a D40 so there's no sensor cleaning function. If I need to provide more info, such as sample images, let me know. Thanks.