I think it's a fault, but both my TV and my Creative PC Speakers are suffering from "fluctuating volume syndrome" where it'll just change the volume level when it wants from loud to quiet. Not in extremes, but enough to make you notice.

They are both analog controls, could it be gunk getting into the mechanism? It's never happened on my TV downstairs which is electronic (I presume), it has a digital display. My knowledge on how volume control works is limited I'm afraid.