I once heard an animal howl at night while camping in Damaraland, Namibia. I never saw the animal. However, I much later stumbled on a webcam footage where some animal (off-camera) sounded exactly the same, cf. see this YouTube video at about minute 3:38. The author of the video claims that it is a spotted hyena (Crocuta crocuta), however, after scouring the web for vocalizations of the spotted hyena, I haven't managed to find that exact same howl. (They typically pitch their "howl" up or down at the end, whereas what I heard had a more or less steady frequency as you can hear from the video.)
Hyenas have a few different kinds of vocalizations. The most well known of these is the cackle/laugh of which there are many recordings and videos. Understandably, it is difficult for a human to get the opportunity to hear the different sounds wild animals make in different circumstances. It is even more difficult to have the opportunity and the gear to make an actual recording of it. So the recordings that are commonly found are the most frequent type of vocalization that the animals make.
I quote below from this Quora answer
Besides the cackle, hyenas make another type of sound A slow, plaintive, drawn out “WHOOooooooOOP”. It’s an essential part of the soundtrack of most African safaris, for it’s the sound you listen to as you lie in your camp at night. This is a bit like a wolf howl in that it lets other members of the group know where each individual is by their distinctive voice as they whoop.
According to other sources, Hyenas are reported to have upto 14 different types of calls from growls to shrieks. Check out this YouTube video of a guy who got real up close with a bunch of hyenas.
I quote again, this time from Thomson Safaris
But what’s that strange, whooping call, like an animal with a slide-whistle lodged in its throat? Or the eerie, low-pitched “oooh” that sounds something like a recording of a space alien being played back at 1/10th the speed? Or the rapid, high-pitched staccato screeching? Didn’t the guide say there were no chimpanzee near this campsite?
Believe it or not, all those strange sounds come from hyena, too. From rumbling bass growls to strange, shrieking squeals, hyena use a wide range of vocalizations to communicate with one another and with other predators.
So, based on listening to the different kinds of vocalizations in the videos linked to here, I am almost certain that's the sound of a hyena. And the sound is not a howl but it is called whoop, in the recording it sounds like an extended whoop.