Weird rattle on cold start, should I be worried or just monitor it?

Every morning my Wrangler makes this brief rattle for about twenty seconds and then it's smooth as anything, but it's been getting slightly more noticeable over the past month and now I'm second guessing every drive. I asked two garages and got completely different answers, one said it's just the lifters priming and nothing to worry about, the other wanted to book it in for a full inspection straight away. I'm in Musaffah so neither is far, but I don't want to be upsold on work I don't need. A guy at work told me to find out more about the Pentastar's common problems after he had a similar noise, though he never actually told me what was wrong with his in the end. Has anyone here had a cold start rattle that turned out to be harmless? Or the opposite, something that started small and got expensive? I'd rather hear real experiences than keep guessing.