Giraffes are weird. They have the longest neck of any mammal - by a lot. And it's long been believed that they couldn't make controlled vocalizations.
It turns out giraffes make quite a bit of noise - in low ranges that humans can barely hear and, for whatever reason, only at night.
It's a vibrant hum that varies in duration and contains numerous notes - so there's definitely some content there. (Scientists are insisting it's just a contact call used when it's too dark to see each other. I'm not convinced).
It's not true infrasound, as humans can hear it if they listen carefully. Probably the highest they can produce with vocal chords that big. (Elephants, on the other hand, communicate in true infrasound and over substantial distances).