Gateway (Router, Modem) is making a loud whining noise

My Xfinity gateway is making a very loud whining noise. I've tried all the usual things, but nothing will shut it up. The device is in the living room and I can hear it from the bedroom. It is loud and high-pitched and crazy-making. The AI Xfinity Assistant is even more crazy-making. I hope that's not the future of AI. I digress. I can't find a customer service phone number anywhere on the web site. Beyond joining the Luddites, I don't know what to do. Many thanks in advance for any help offered.