I'm a technician for Comcast. Most likely either the drop to your house has gone bad or maybe a bad fitting. Cable is radio frequency, so if you have a cut in your drop, squirrel chew (in aerial drops), etc. it lets interference in, which alters the wave lengths causing tiling and loss of internet. This is known as ingress, or signal getting into your cable system. A trouble call is likely the only fix to check for ingress and possibly replace your drop