Yowling day and night

We adopted this ginger boy 6 months ago. Since month 2, he yowls (not meows—MUCH louder than that) nonstop. Day and night.

He is routinely fed, gets fresh water twice a day, has a clean litter box, has a soft window seat for him to look out, has plenty of toys. He seems lonely but doesn’t want to be touched. I work from home frequently and work in the room that he stays in. He has free range of the house when he chooses.

WHY IS HE YOWLING?! What do these noises mean? Bored? Sick? Happy? Lonely? I am going batty. Am I doing something wrong? This video is a VERY mild version of his normal behavior. Please help!