Sounds like a Kenwood Nexedge control channel on 450.3125. I used to show this as the Engineering frequency for KABC TV 7. Also getting digital on 450.125 (fair), 450.325 (strong), 450.1625 (strong), 450.1375 (fair).
" The pilot carrier is approximately 310 kHz (.31 MHz) above the lower band edge. The exact frequency used may vary because the transmitted signal may be offset slightly to reduce interference" - taken from this website @ Television Frequencies - The RadioReference Wiki