According to the Committee for Jewish Music:

"The main part of the music should be the melody. Percussion should be secondary. They should not bend notes electronically and should not use instruments like electric guitars, bass guitars or saxophones in Jewish music."

Rabbi Luft is especially disturbed by Jewish Rock music "where the dangerous beat plays more of a part than the melody, has no place in a society where people are trying to keep their moral standards high.”

HT: Hilary. Source: BBC: Rabbis black-list non-kosher music