Truly Thanks! You've eased my conscience although thinking about it, I don't think I was being given a choice. I guessed, with so many, you would have seen this before. I've only ever heard that trilling used by a female to her kittens. (cooing like a wood pigeon for those who don't know)
So, I guess we can assume he knows all the words to Oklahoma :-)
RESPONSE:
You are very welcome! And congrats on the new addition to your family! Trilling is a happy sound and cats trill for many reasons. We love it when a cat trills at us. It's almost better than a contented purr!!!