The engine doesn't so much grow quiet as fade off after a final (and brief) rev of confirmation, then allowed to trail in to silence. Yes, it's him.

If only he were better at reading human emotions, though- she seems to be relieved, were he any guess.

Still a friend, then.

After a few long moments, he lets his driver's side door open. He's in no state to simply drive off [not without causing far more trouble than it's worth], but not knowing if anyone else is nearby- he's uncertain whether it's safe enough to risk talking aloud. Normally he'd simply transform, but these are hardly normal times.

Even by Earth standards.

Within the cab, his radio crackles to life, for the moment only offering a bit of static- but she's smart, isn't she? She'll catch the implications.