Common LCD related issue on ThinkPad T30

I have 3 IBM ThinkPad T30 notebooks; they all have a common LCD related issue. Their LCD backlight is flashing in a random manner. It doesn’t turn itself off, just gets a little bit dimmer. It’s barely visible when something is moving on the screen (like movies and games), but its very annoying viewing the desktop. First I thought that it’s
synchronized with HDD activity, but it turned out, that it isn’t. I disassembled all of them (removing the motherboard too) and put them back together (there were no noticeable damages), but the symptom stayed. I figure it has something to do either with the backlight bulb, or the inverter, or a general power problem.

Any suggestions or help is much appreciated.

When I have to fix a laptop backlight problem, I always start with reseating connectors on the FL inverter board and then replacing the inverter with a test one. Very often just reseating itself helps a lot.
Try to reseat connectors on the inverter board. You can use ProGold connector enhancer to improve connector conductivity. IBM ThinkPad T30 service manual has instructions for taking apart LCD screen assembly. If it doesn’t help, I would check what version of BIOS you have installed and search on IBM website for the latest version (actually I would try it before opening up the laptop display assembly). It’s possible that newer BIOS version has a fix for the backlight problem. If it still doesn’t help, I would try replacing the inverter board. You have good chances that it will fix the backlight problem. Fortunately, new inverters for IBM ThinkPad T30 notebooks are cheap.
BTW, I assume that you have tried reinstalling the video driver already. Just in case.