TV Reception has the Hic-cups

[Bob Cicerchi]

My TV reception has the hic-cups. My system is a HD roof antenna (Winegard HD8200U) with a preamp (Winegard Chromstar 2000). The signal goes through a converter box so that I can use my analog TV.
Reception is always good with or without any hic-cups. Some days it has the hic-cups on about one half of the channels. The hic-cups may be rapid, slow, or random in it's spacing. The hic-cups are not restricted to the same channels.
I am receiving a strong signal with the transmitting stations in the range of 45-90 miles. There are no trees, hills, or buildings in the reception path (for miles). I have no idea what to do next.
Any ideas? Bob