Oh sweetie! It's totally normal and it's just a phase - I promise you he'll stop it soon and move onto something else

My DS is the same age as yours and he's going through this as well. I also remember it with DD and it only lasted a little while.
You don't need to do anything to discourage him, he's just testing out his vocal chords and soon he'll discover something else and this will all be a fond memory. He's far too young to be worrying about manipulative behaviour yet, he's just working out what his voice can do.

I especially love it when DS starts up his squeaking at 5am and wakes up his sister - and then he promptly goes back to sleep leaving me to deal with the consequences! Little turd LOL.