I also have a Philips LCD TV, and have twice had the situation where audio dropped out. Changing channels did not help. Turning both the Cisco and TV on and off (multiple times) did not help.
The problem did start when I switched channel, but I don't recall if I was switching away from a DD channel. However I'm pretty sure I went back to the original channel while trying to fix the problem. Next time I'll pay more attention.
In both cases I resolved the situation by unplugging the Cisco's power cord, waiting a few seconds, and then plugging it back in again. (This seems to be the only way to truly reboot the unit. It seems harmless, unless of-course you have something recording—who knows what that might do.)