The lens is not the issue. Some d600's have an unusual amount of internal debris and lubricant that is splattered on th sensor. If you own a D600 and wish to bravely find out the truth, place your d600 in manual focus/jpeg basic/CL/manual/shutter speed 2000 and keep shooting in 5fps till you reach around 1500-2000 shots and now shoot a plain background at f16-f22 to expose what is on the sensor. If you have the issue you will know it right away. If you dont you are lucky. Just so you know, if you do have the issue, you will need a wet cleaning after doing this. You will have lubricant and dust splattered all over the sensor. This is one way to get tid of some of the over lubrication and debris and will take a long time to go away. The kit lens can cause normal dust to enter the camera as you zoom in and out, but this is internal issue of the body from the factory and lack of quality control. It will reduce over time since the camera only has a certain amount of lubricant and debris inside. The issue is for some people that can mean a long long time.
Edited 5 months ago by Nikonfan99