It probably needs to just be 'run in', hopefully...

Obviously, if it's still grumbling (or worse, failed) after a couple of dozen miles, then it'll be a warranty issue.

I'm always surprised by how many people find that their new hubs are under-greased and quite often too-tightly adjusted. I can understand the too-tightness a bit, as presumably they do it as a hedge against them 'loosening up' after being bedded in, and knowing that 99% of riders will not think to, and/or not have the knowledge to check them for tightness, but surely if anyone can afford to put enough grease in at the factory, Shimano can...?