Cat whines all night long!?

I have a neutered 8 year old male cat who hollers every single night! He likes to do so once I've gone to bed and he's VERY loud about it. I've read many posts about being lonely, but my bedroom door is open and he'll even jump in bed, stay for 2 seconds and leave again to keep whining. He's starting to do it before bedtime now. I thought maybe he was missing the company of a cat so I got 2 kittens to keep him company. He seems to have adjusted well with them. He doesn't fight them when it's feeding time, he's fine sharing his litter box and even snuggles with them on the couch sometimes. Yet it hasn't curbed his whining at night. His box is clean, he has fresh food and water and as I said before, my door is open. What else can I do? I'm losing sleep and I can't take it anymore! I live on a busy street so putting him outside is out of the question. HELP ME!!!