Scumcast has dual-DVRs that mute the audio if the DVR has to power itself on to record a program. Their "customer service" people's preferred method of clearing the alternate mute was to pull the power on the DVR. Here's a more useful solution:

To assign the alternate mute function to a button:

Press the cable button; press and hold the setup button until the cable button flashes twice; enter 994; press setup; enter 00141; press the button to which you want to assign the alternate mute function (the cable button will flash twice).

To assign the 30-second skip ahead function to a button:

Press the cable button; press and hold the setup button until the cable button flashes twice; enter 994; press setup; enter 00173; press the button to which you want to assign the 30-second skip ahead function (the cable button will flash twice).

To restore a button to its default function (e.g., you messed up):

Press the cable button; press and hold the setup button until the cable button flashes twice; enter 994; press the button you want to restore twice (the cable button will flash twice).

Update

If you have a newer remote (bronze), you may have to get to to behave as though it were an older remote (silver).