Replying to Comcast Cable Box

So i have a comcast cable box attached to my tv and frequently it will get really fuzzy and these lines will go up and down across the screen. Every once in a while, it will even go full fuzzy to the "snowstorm" screen. All i have to do is go up to the back of the TV and tweak the cord to the side a little for it to go back to normal but its a hassle to do every couple minutes. Anybody know what the problem is? I don't think its a loose cord because i've tightened it as much as i could with a wrench