... I converted to fiber a few years ago, including adding fiber to the home for ISP services. Then about a year ago, Emile suggested they preferred copper into the Extreme, so I reverted and tested copper. I'm not 100% sure if there is a substantive difference: they both sound excellent. But I left it on the copper.
It makes sense that each conversion would be a potential source for *noise* but there are probably many links in the chain that determine the final signal quality in each network.
I live in a US city in the NE, condo, lots of RF and EMI nearby, so fiber seemed a logical choice. It was great, but perhaps not definitive as an improvement. I pulled fiber and copper at time of install, so switching was/is easy for testing. I certainly don't mind not needing the FMCs, SFPs and power gear!