Engine rattle sound under load?

Hi everyone, maybe I'm just being too paranoid, but today I drove my 2006 G2 Prius with 59,000 miles to the park and had the windows down. I climbed a hill for a good while that had the engine under load and there was a concrete wall beside me, and I could hear a very very faint metallic-like rattle. I mentioned it to my partner who listened and said he couldn't even hear it, so maybe it is just me.

I always use Exxon gas, and the oil was just changed last month with Mobile 1. I don't think the heat shield is loose? Hmm. Or maybe the 1.5 just sounds tickety compared to the G3 I have.