[Ruminator]

They are all different in a lot of ways.

Thats alot of great interaction with you, the singing.
Does he revert to the singing, etc. if you are playing trucks and cars with him? He might yet be a little young though for this?
My boys around that age liked me to make tons of sounds with the trucks and cars as we played on the floor driving the little toys around.
I made air brake hissing sounds, motor revving sounds as I moved the truck or car, and lowering my voice to change it said things like, "Bye Joshy, I'm going to work now." as I 'drove' the car to where I had a truck parked in a different place on the floor.
They loved that interaction with me.

He is at a very sing-song age. They love to have their parents sing to them at this time. Try mixing it up with some other songs for him that would appeal to him like Old McDonald Had A Farm, you can really have a lot of fun with this song as you make exaggerated animal noises and mix in some laughing and giggling with him.
I remember lightly poking my boys on their chest and belly and laughing while singing the part of- "with a moo, moo here(poke), and a moo, moo there(poke), ... you get the idea.
Is his singing behavior maybe just his means of interacting relationally with you right now? He may just really need time with his dad as far as the singing goes.
Are you gone for extended times due to work where he would develop longing for you?
Some of the other stuff though, I don't know Clod. The bolting could just be headstrong bad behavior. What are his consequences for it?

But I agree with the others, definitely ask about it.