This is quite old. It was
commonplace among owners of
Acorn's
BBC Model B home computer.
After hanging onto your PSU an extended sideways RAM board, a shadow ROM board with some 10 ROMs, maybe a 5.25" floppy disk drive (and we're talking about old kit here, full-height or double height drives!), and leaving it on for a few hours, things would get a little warm. Hot even. In fact, so hot you could smell the plastic...
The reason was fairly simple: the PSU had grilles in the case, but no fan. Or, as we say in the computer case business, it employed a passive cooling system.
The solution was also fairly easy: you'd drill holes in the case, right above the PSU. Normal people drilled to form a bitmap of the BBC owl (and maybe even hung some mesh from below, to prevent things from falling in; people with two left hands (like myself) employed a more creative technique and drilled along a complex chaotic irregular pattern. The end result was the same -- a noticeably cooler case.
Oh, and do yourself a favour and buy disk drives with their own PSU; the beeb's isn't really up to driving a motor...