said by Arctucas :Regarding your comment about noise on the coax, could you provide some examples of possible devices, and what methods to use to determine if that is the cause of the intermittent dropouts and signal level fluctuations?
Any device that is hooked up to the coax in your home could potentially be defective, and generate noise, but this is a very rare occurrence. Things like this are often an issue outside, between the pole/pedestal and the house, so that is a very good place to start. I was simply mentioning the other potential issues to give you somewhere to work off of should the outside lines check out, or if you still have issues after replacing them.