toy4two2,

I'm sorry to hear that you're having this issue.

If the problem happens with the one specific input, it may be an issue with the tuner. However, without inspecting it, it'd difficult to determine what is causing the issue.

Assuming that there are no speakers or devices directly next to the channel up/down buttons near the bezel, I'd recommend having the unit inspected by a technician to give you a diagnosis.

--HDTech