DCT700 Audio Dropouts on ABC and CBS in Pittsburgh, PA

Experiencing intermittent audio dropouts for ABC (WTAE, COZI) and CBS (KDKA, WPCW) in Pittsburgh PA using DCT700 set-top box.  On Demand programming for same channels is flawless.  Picture is clear on all channels including four channels experiencing audio dropouts.  Have performed trouble shooting including checking connections, trying multiple combinations in DCT700 audio setup, and sending numerous refresh signals.  Finally, no issues with Xfinity Stream, Blast Internet or Voice. 

Why does audio dropout issue only occur with ABC, CBS and their local affiliates? This problem makes it difficult to watch programming on these channels.