I was in a house with metal roofing...and I noticed it was louder when it was raining. Like I could hear it hitting the roof more than a "normal" roof. Not lots...but enough to notice.
A friend of ours built a house a few years ago and went with a metal roof. I haven't been there when it's raining, but he's commented that it can get pretty loud. But it's also a flat roof (no attic or trusses with airspace) so might be louder than with traditional roof construction.
And, now that I think about it, we had a metal roof in our last place. Not the usual flat sheets of metal (standing seam), but more like shingles that were made of metal instead of fiberglass (or whatever they make shingles out of.)
That roof looked great and was supposed to last 50 years, but of course we sold the place 15 years later. I hope the new owner is enjoying the money I spent.