I've had a couple no-starts where my engine wouldn't start on first crank when my engine was hot. I don't think it's much to worry about it besides something being out of range the moment you tried to start it again.
Injection sound is what makes up 90% of engine bay noise. You should just listen to the engine in different settings and states. I test mine every morning, doing different revs taking note of the injector and exhaust-sound feedback. I drive off down the road a couple minutes, pull over and park somewhere where I can hear the engine, listen for injector changeover.
You can also get a long screwdriver or long metal probe and listen to the injectors. I use a flexible claw grabber like pic:
Very easy to listen to the injector pulses. You can also listen in on the valvetrain clicking away (it is very quiet and smooth).