Oldest dated cite I’ve been able to find so far is 1991. The column doesn’t show a publication date, which usually means it’s pretty old … Then again, what’s the point of being the world’s smartest human being if you have to wait for other people to discover things to give correct answers?
In fairness to Uncle Cec, the question wasn’t about whether giraffes make sounds, so it was a bit of a toss-off comment. That said, one paper I ran across was researching the production of infrasound by giraffes. Very low-frequency sound can carry over extremely long distances even with low volume & energy requirements, though it can’t carry a lot of information. It was first discovered in use by elephants, and other animals (including giraffes) are now known to produce it. According to that paper, the mechanism by which these sounds are made isn’t yet understood … and the sinuses are one of the organs that have been suggested as potential sources for infrasound production. Could be-clearly vestigial in humans, as we neither produce nor are able to detect infrasound (not without a microphone and an oscilloscope, anyway). But maybe our distant ancestors called to each other over distances of miles with these deep rumblings. When they were out of their cellphone coverage areas, of course.