iOS 9.3.5 update issues

Just installed 9.3.5 (13G36) on my iPhone 4S which was working OK beforehand. Now music sounds really weird, for example, Cee Lo Green´s "Bright Lights Bigger City" sounds as if he is singing behind a bathroom door but the instrumentation part seems OK. Any ideas as to what the problem might be? Is this a hardware fault brought upon by the software upgrade?

Message was edited by: userfrombarcelona Ah! The problem was the earphones! With other earphones the sound is perfect!