although another monitor flicker when the monitor tears.
I assume that you mean "the 2nd monitor flickers under the same conditions that the 1st monitor tears", or are you saying that you have tried 3 separate monitors, all with different behavior?
Take your time and walk through all the steps that folks have laid out for you in these comments, and try to answer each question we're asking. There just isn't enough detail for us to give solid answers or further suggestions.