I have the left speaker dropping out intermittently. It seems to be occurring after a boatload of updates (including a kernel update) today. I am sure it is Ubuntu problem and not a hardware fault because using another input device it works OK. I can still hear a very faint sound from the left speaker, it is almost as if the balance is shifted very far to the right (but I checked that slider, it's in the center).
I think I'm experiencing the same. I'll put my hardware details below to make it easier for others to find this. Here is how I fix it:
When the balance is shifted to the right, I hear only a very weak sound on the left side. I can take countermeasures by adjusting the balance in the sound-menu to the left. However, sometimes the left side is completely dead. I discovered that raising the volume dramatically brings the sound back on both sides. Same loudness on both ears. I have to move the slider for the volume at least 80% up (to the left). CAUTION: if you use headphones this will blow your drums. So better take them out. I need to do this for one second or so. Not longer. This is strange, it feels like something is stuck in a pipe and applying more pressure helps to push it through - although we are talking about drivers and hardware of a computer. Anyway, try it! I have not permanent fix. The balance shifts to left again after a reboot. Not always, but randomly. Then I just repeat the procedure.
I also found out about Bug # 106945 which describes also a problem with the balance, but is from 2007 and obviously fixed.
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