It sounds as if either the panel buttons are stuck on the TV (volume, channel change, power etc.), possibly a stuck remote button or there is also a possibility that it may be an internal issue. Unfortunately, without being able to inspect the unit, it's difficult to diagnose. I might suggest calling 800-SAMSUNG to see if the Samsung customer service center might be able to assist with further troubleshooting or set up the necessary repair.
The TV will switch from the cable source mode to TV without a prompt and will then cycle through chanels. The only way to stop the process is to unplug the tv from the power source. It also will randomly cycle through the menu if options if in them. It makes a beeping noise if you attempt to push any buttons while this process is happening. It will do this several times in a row and then not do it again for days.