He's trying not to tremble now; Starscream can feel Megatron approach, feel his eyes on him. He does take some offense at that statement... He put his whole soul into that song just now, geez.

"Your critique is noted, my liege... not that I usually make a habit, of singing, as such, but..." he quirks his vocaliser nervously. "I was going to bring him back to you, naturally. What else would he be worth keeping around for?"

He knows that's a terrible lie, and one that Megatron won't believe for a second, but he's hoping that maybe if he's lucky, he might get let off the hook, seeing as he just did something incredibly useful here... even if his intentions for doing so weren't exactly innocent.