[Signals] Signal Check Please

Hi All! Over the last part of a year I have been watching my signal levels drop from approx 0/-1dBm Downstream to now -10/-11dBm. I have called COMCAST repeatedly but the people on the other end of the phone claim my signals looks okay to them and was curious what you all thought and maybe if something needs to be done how to go about motivating COMCAST to do something. Thanks, Dan