I'm sorry to hear that you are having problems when changing the response rate on your PX2370.
Please know that the response time is 2ms in "Normal" setting.
There are several possibilities as to why you are experiencing the artifacts when switching modes. This can possibly be corrected by turning your V-Sync option on (if available), but V-Sync may not be available on all games/programs (if that is even the problem).
To better address your issue and to walk you through a possible solution, please contact Samsung Customer Support toll-free at 1-800-726-7864.
when i change the response rate there are 3 visible horizontal lines just like this on the video http://www.youtube.com/watch?v=lB13Cud1yec, i did notice it on fast motion video so i did change the response time,btw the led is 2 days old still out of the box