The first time for me was with their T43. This model was mostly a platform refresh of the T42. There's a chip called a southbridge that's located below the palmrest. Between the models this chip went from 400mhz to 533mhz. Lenovo decided it wasn't important to improve the cooling, no heatsink whatsoever included on the southbridge. However, they kept ample temp sensors in the case so the fans would pulse nonstop as it failed to cool this one chip.
I had two nicknames for that laptop. The 'nut roaster' and the 'vacuum cleaner'. I eventually fixed the problem by hammering out an old copper penny and sticking with thermal compound to bridge the gap between the heatsink and chip. It wasn't perfect but it dropped the temps like 10C. The rest could be controlled with an installed fan daemon.