No sound on Sansui LCD TV

I have Sansui 32" LCD TV, but no sound on 50% of channels, whichever frequency is below 300 MHz, there is no sound on channels, im using cable, but same cable is working fine on computer (i.e thru tv tuner card), can anybody help me plzzzz
thanks

It sounds like you got a lemon, you should take it back to where you got it from. Or if you've had it for a while, contact the manufacturer to get it repaired. Something as simple as a dead capacitor could cause something like that.