A rift in the lute

My wife and I frequently do the cryptic crossword that appears daily in our newspaper. Some days it can be so straightforward it's done in a quarter of an hour. Other days some of the clues seem incomprehensible, much more like the ones that appear with the Saturday cryptic, which is much harder - though we've found it more doable as the years go by. 

Yesterday we got stuck with a clue that we just couldn't make head or tail of. The clue was "Musical version of someone rocking the bo...