Hey guys, out of the blue something weird started happening. When i would press the up and down volume keys on the keyboard, no sound is coming out. When i raise or lower the volume from the top status bar, that little click is audible, but when i press the up and down keys from the keyboard, no sound comes out. is this a hardware problem? will apple replace/fix this? could i have muted it or something or is this like i said, a hardware problem?