Starscream has a very bad (or possibly good) habit of not trusting anyone -- which does, of course, include Rung. Usually he would deal with that by just eliminating the source of his mistrust.

But people would notice if Rung just suddenly went missing. And besides people had a habit of coming back to life.

And that wouldn't solve anything either.

Blasted place.

Finally ...

"You know that's distracting," he said as he idly changed the subject and gestured a hand towards the spark window on Rung's chest.