Is this a separate Roku device, or a tv with Roku built in? What is the Roku model and model number? Does this happen on all inputs?
Without more to go on, this sounds like a television equipment problem to me. For that you need to go to the television manufacturer. Even for Roku TVs, Roku just supplies the operating system, the hardware is the manufacturer's responsibility.
Roku Streaming Stick +, 3810X, Ser YH0059427035, wifi - Samsung UN55ES6100
Roku Streaming Stick, 3600X, Ser 5S56D8240827, wifi - JVC EM37T