4am Howling

My 3-year-old cat, Jayne, has recently taken to whining throughout the day in loud wails that are especially annoying. During the day it wouldn't bother me, but he also starts up at 4am, waking myself and my husband, and keeping us awake.
   
Jayne is male, fixed, and an indoor cat. He has never been outside since he was rescued by an animal shelter. Sometimes when he whines, I give him fresh water from the tap, but usually that isn't what he needs: he just starts up again. He always has food on the floor that he can eat. He has access to the litter box 24/7. If I give him pets, he will stop for a while but within half an hour he will start up again.
   
I have four other cats, and none of them are acting this way. I'm pretty much at my wits end with this, and I need advice on how to deal with it. We've tried sequestering him in a large, walk-in closet because that worked before when he was being mischievous, but it is not working now. I'm about to buy some kind of training collar, but I'm not even sure that will work.
   
Please help!

Is there a particular reason that your cat is not allowed outside .he probably is bored out of his mind and wants to do what is very natural to any cat and spend some time outside . At four am he may hear other cats in the neighbourhood and is eager to see what's going on . I don't think that putting your cat in a wardrobe will achieve anything . Cats do not understand that you are trying to punish it for bad behaviour.
   
Perhaps if you are worried about letting your cat to spend time outdoors unsupervised you could consider providing your cat with a penned outdoor area .
   
Hope this helps
   
Linda