The Hamlet Project

What is the origin of this expression? Is it related to the harp? Because of all the relentless instruments to choose from, this one would seem to be the least intrusive. I’d have thought still bag-piping on my daughter, or trumpeting or drumming (where we get banging on about my daughter, perhaps) or dijereedoo-ing on my daughter or even bassoning on my daughter. But harping, well, a harp evokes a quiet, melodic sense, repetitive, possibly, by not so’s you’d really notice.
Unless it’s a jaw harp. Those things are relentless, repetitive and irritating.