I've had this from bad earbuds--I'd only hear part of the music which would sound like it was coming from the back of a deep cave. Granted, I usually buy rather inexpensive earbuds, but still you expect these things to work right. And usually they do. But I had to replace my last pair because the connecting end didn't make the proper contact with the jack, unless I rotated the connection point to be just so. I usually use a right-angle adapter, or even two of them, so at first I thought that was the culprit. But no; other old headphones we have lying around the house worked fine.
It was ridiculous and totally unacceptable, and a shame besides, because apart from the main issue of not working right, that set of earbuds was well made, with sturdy cables I wouldn't have had to worry about breaking or wearing out. If only they'd worked right.