The singing part of a song just doesn't go away like that. Its not like its a Photoshop layer, where the vocals are on layer 1 and instrumental on layer 2. Therefore if the vocals are cutting off, does the instrumental sound different? You can get rid of vocals by messing with the EQ's, however in most cases the instrumental will sound different. Therefore I think it is a problem with your hardware, as in a problem with the computer chips.