White lines on screen

Re: Samsung 40" HD TV - older model (around 10 years old). 1080p.

When my tv is on I get these vertical streaks/white lines - reminds me of static on old televisions. Sometimes the lines are so heavy they almost completely obscure the screen, other times they are gone or not too many. I don't seem to have them when I use my DVD player, but I use Amazon Fire Stick or Roku for almost all my viewing, and the lines are quite noticeable with these devices. I don't get cable or satellite, so I don't know how that would affect the problem.

I suspect the problem is with the HDMI connectors on the tv, but I have no idea and no way to check or replace them. Has anyone else had this problem? Any thoughts about whether this is fixable and how to do it?