My speaker balance (System Preferences/Sound/Output) seems to have a mind of it's own. Even if I centre the balance, it drifts out to the left over a period of time. If I shut the machine (I-Mac 17") down with a centred balance, it always restarts with left speaker louder. Any ideas? Also (while I'm on), is there any reason for my machine to be slow (ie delayed action of a few seconds using volume control) following a few hours of screensavers? I've tried a number of different savers (from a magazine disc) all with same effect. Only solution is a restart. Thanks!