I think generally everything said here is correct.
Startup rattle is normal to a point, but depends on how long and how severe. As for how often do they go? Well, I think its rather a lot more than just a random event, BUT the internet being as it is, you always hear the bad, and never the good.
And lets be honest, how many cars out there are plagued with issues such as these..........****** loads. Best thing to do, is to not worry about it, otherwise you'll worry yourself into selling it (which I've nearly done before lol)