Nexus 5x charging noises and screen illumination.

Hi ya, I recently bought a Nexus 5x.
Whenever I put it on charge with a low battery goes "bu-du-bump" every few minutes for no reason.

also, everytime I have it on charge, the phone lights up every few minutes. Which is a pain when your trying to sleep!

Any clue as to what it is up to please? Or if I can stop it?

Many thanks :D