Faint rattle noise while acceleration?

I have a 2006 Hyundai Accent with 40000 miles on it, the car is perfect and runs very nicely, no issues at all. Yet I've noticed a very faint rattling sound while I press on the accelerator, very faint, but still there. I use the proper 87 octane gasoline, so that shouldn't be the problem. What could be making this sound, and should I be worried?