May need a spectrum analyzer
If you can get access to a spectrum analyzer you can check the cable for signal level and noise. One problem I had with Mediacom was the signal level was very low and there was so much noise on the line that it almost completely swamped out the signal. They had some nice equipment but nobody who seemed to know how to use it. I showed the cable guy the problem on my own analyzer and got them to turn up the signal level which helped for a few days but then it went back to not working again. One problem with cable is that if you have a white trash trailer park down the street they have probably tapped into the cable illegally which interferes with your signal. Everytime the cable guy from Mediacom came out to my house they were always saying they had to remove illegal connections down the street!