I don't know if this means I've got good or bad headphones, but since I've gotten some new earbuds, I've been able to hear "ts-" or "s-o", basically the hissing S sound, from higher pitched singers as a high pitched noise. Words and all are pronounced perfectly, just that you can hear the "tsk" as they sing into the mic. Sort of off-putting.
The songs aren't crappy quality neither, so that shouldn't be the problem.