Horizontal lines on my VIZIO TV

over the past several days I've had horizontal lines going from bottom to the top of my VIZIO tv screen (TV is less than 2 years old).  Prior to this, the TV signal would flip flop between HDMI and "normal".  Doesn't matter if I'm watching comcast channels or other streaming apps.  I've replaced all cables and reset the system multiple times.  I just found out that the modem I have (from comcast) is no longer supported so I've ordered an more up to date one from comcast.  My question is does this sound like an issue with comcast equipment or the TV itself.  Any help would be appreciated.  Thank you.