You could try to install chokes on the line cross-connects into the system. Sometimes that can be an issue. Also make sure that you have a good earth ground on the KSU. Also, I have had troubles every now and then with "Hot" lines from the CO. You can check with a line Db meter. Or, you can also try swapping CO cards around in the system and see if the trouble follows the CO cards or stays with the lines themselves.

Thanks