Oh heavens, a yorkie/maltese mix, must be the cutest little thing ever. I have a maltese.
What your little guy is doing is playing. Puppies need play time, so he is entertaining himself. They have tons of energy and then bam, they know when it's nap time.
Get a ball, or something that the both of you can play with. This will get him some play time and teach him some skills and have human contact.
Love and play with your new guy.
I caution you, please not too many treats. Yes, they love them, but the best treat you can give them is your love. It is more important that they eat their food and get the nutrients they need at this age, then treats.
When training them, treats are fine to reward, but please not too many. I am sure you guy is a little guy, and he will get all filled up on treats, and then have no interest for his food.
Play with him, love him and enjoy him. And give him a big hug for me
He sounds like a healthy pup, and those are just playful sounds you hear.
Congratualtions on your new addition !!!