Howling cat drives us crazy

Max is a friendly, neutered male cat. A typical cat suck-up, he's spent his life sitting on laps for exactly as long as he wants (and not a second more), eating, prowling the neighbourhood, and, of course sleeping. Now, at 17, he's acquired a weird habit: howling. He's very healthy; most people are shocked to hear he's so old, and his vet is constantly astonished at his good condition. We keep him brushed and clean, and spend lots of time with him.
But the howling!! Sometimes he sounds like someone's pulling his intestines out of his caboose, or clamping his tail in a vise. Other times, he sounds like he's depressed and on the verge of hurling himself off the roof. My wife says he's howling for his ancestors to come get him, like a Klingon.
As soon as someone sits down, however, he jumps on their laps and purrs like a kitten. He never howls when he's being petted.
The trouble is, he howls all night. At 3 am, I'm tempted to let him outside (he stays in at night) to play with the coyotes. In the day, when he's outside, he sits under the cedar hedge and howls.
The vet says he's fine: no bowel obstruction, no urininary tract problems, no source of pain. He prescribed cat valium, but it only makes poor Max into a zombie, which is even worse.
Does anyone have any suggestions?

A couple of suggestions.

Try using a nightlight. I have 3 in my apartment. Also, there are times when my cats (6 of them) want to get frisky at 11 p.m. (my downstairs neighbor does not appreciate this). I give them a little catnip.

Have his eyes and hearing been checked lately?? It could be that one of those senses may be deteriorating.

He might just be lonely. Where does he sleep? Try putting a kitty bed in your room so he knows where you are and feels more secure.

Other than that, I don't know what to tell you, especially if he has a clean bill of health. Good luck.

Did the vet do a total body function blood test? If not, you may want to look into that. If they did and all is okay health wise, it sounds as if he is probably getting senile and insecure. He may be getting confused and he is just letting it show verbally. As Donna said, I would probably keep some light on at night and I would limit his outdoor time. You can also try leaving the radio on at night for some background noise.

My 18 year old did that as well. I don't know if it was due to health problems, but she had kydney failure and bad teeth. So, I guess it could have been her age, her illnesses, or that she would get lonely at night and just forget where to find us.

Good luck!