Motherboard rear speaker jack

I bought the Gigabyte EP31-DS3L about 6 months ago and yesterday, the speakers connected through the green speaker jack at the back, only output sound through one channel (the left channel) and if it is connected to the case's front panel jack, both channels work. The day before there was some crackling/noise on the right channel, so this seems to me like a hardware fault? I have tested with other speakers and headphones through the back, which only output through one channel, but work fine at the front panel connector. I am using some recent drivers (Realtek 2.30) from the realtek website.