The site discovered the issue after placing the HomePod on an oiled butcher-block countertop and later on a wooden side table. Other reviewers and customers have reported the same problem.
Apple says “the marks can improve over several days after the speaker is removed from the wood surface” and if they don’t fade on their own, you can basically just go refinish the furniture—the exact advice Apple gave in an email to Wirecutter was to “try cleaning the surface with the manufacturer’s suggested oiling method.”
WireCutter notes that they haven't experienced this problem on glass, granite, nice MDF, polyurethane sealed wood, or IKEA bookcases. The HomePod was tested in the same place a Sonos One resides and it hadn't caused any damage in months.
It's unclear why exactly the HomePod is causing these rings. Please follow iClarified on Twitter, Facebook, Google+, or RSS for updates.
@Dr_Seamus: "Can confirm that #HomePod leaves a white ring on wooden furniture! Luckily we don't care about this crap TV unit. Others may not be so lucky."