I have a 2 year old Toshiba MD13Q41 or MD20Q41 TV with DVD player that
has little or no sound on some channels and perfect sound on others.
Picture is fine on all. Some channels have this problem all the time,
others never have it, while some have it intermittently. When there
is little or know sound there is sometimes a faint crackling sound or
small amount of 60Hz hum.

Any ideas?