I would start by moving the antenna to the chimley, This may not give you much more signal, but the signal will be cleaner. That antenna could be picking up "ground noise" at only seven feet off the ground. That will cause the problems that you are experencing. While moving you might as well replace the coax with one run of RG6 and be sure that your balun is dry. Another thing that may help would be to use a ground block in the coax line to connect your coax to your house ground. This not only protects you from lightning but also can eliminate some sources of interference. As for the amplifier, the Channel Master CM3414 is a good choice. I recomend that you look at chimley mounts by Ronard at
www.solidsignals.com. Tune to 166 magnetic and rescan for digital channels. Should work great!