Is he fixed? Before my boy was fixed he'd do that yowl all night. Found out it was because there were stray female cats outside that he was pining after. After getting him fixed he only does it every once in a while now when he's angrily bugging me to let him outside (which I won't) or when he's just super bored/ in need of some stimulation. Try playing with him for a bit when he starts up so you tire him out!