Are you running fraps to verify FPS rates?
If so, when you see the tearing, does the FPS drop at all, or does it stay consistent?
If the FPS drops, then it could be a host of issues. If it remains at approximately the same rate, you're going to have a lot less to explore.
Quite frankly, if you've replaced everything - and the monitor is the only thing that would be an issue if the FPS is staying up - then there is (as others have suggested) the chance of nearby sources for the disruption. That, or your brain is screwy. I know that may sound odd, but you could have something going on in your brain that is causing you to notice the change. What that would be, how to fix it and/or where to figure it out - well, I've got no clue. But I know that vibrations and flickering lights can modify our perception of what we see in front of us.
Additionally, 30fps is only -sometimes- adequate. It'll provide smooth gameplay, but can have some issues especially when you're rapidly moving the on game view. The connection to the monitor can change things, as well as the scan. Progressive vs interlaced, for example, can have an impact.
If you find that the frame rate temporarily drops, there could be a few issues. First, if you enter the game quickly and do something that would occasionally cause the stutter, will it do it, or will it not do it till later? If it is delayed in start, then it may be a heat related issue.
If you're looking for the source, run something like speccy for the processor core temps (speedfan works, but speccy will give you a much easier graph to look at, speedfan will let you do that as well, but you have to stay on the page and you can't change much). If the GPU is of concern, GPU-Z can monitor things more in depth. You can even have it report the reason for capping the performance, identifying it as power (raw power, not voltage, AFAIK), utilization, temp and a few others. I used it to diagnose whether it was my GPU or CPU that was overheating so that I could adjust the demand on that piece to allow for more smooth gameplay.
One other thing - have you tried knocking the settings down really low to ensure that your machine will be able to handle it without overheating or reaching its maximum?
Anyway, have you checked the FPS rate with fraps? That's the biggest thing to check ATM.