This is actually quite a common problem for this generation of laptop from IBM. The T4x series have an issue with the internal GPU coming ‘loose’ from the motherboard over time, usually increasing the problem when you lift the unit from the palmrest area. The only way to fully repair this would be a reflow job or motherboard replacement, but many people have found temporary fixes by applying pressure to the GPU, etc.
[https://forum.thinkpads.com/viewtopic.php?t=74366|There is a good post about it on the ThinkPad Forums] that I’d recommend checking out.