I have a new bike and it?s really noisy back there and only with weight on it. I?m a little reluctant to tighten them more right from the factory.
The factory may have been sloppy installing/tightening them, so you should check them out or have a shop do it. I'm no expert on this topic, but there are many vids out there, including a couple Rad-specific ones, about how. Just do it in tiny increments and make sure to balance on both sides.
At a minimum, pluck them like a harp string or tap with the shaft of a screwdriver - if they're dull, flat-sounding and don't 'sing' they could probably stand a bit of tightening - if loose, definitely. If the noise you're hearing is 'clicking', that's probably it. Make sure to use the correct size spoke wrench to avoid damaging the flats on the nipples.