My 704 today started making a squealing noise when playing some particularly bad movies (film-wise, not that there was anything wrong with the discs themselves ). It seems to come and go, but I'm guessing something is either failing or needs to be lubricated. Ideas?

This usually means it's time to replace the spindle motor. (And no, the motor can't tell the difference between a "good" movie and a "bad" movie )

Since it doesn't do it all the time (and actually seems to have stopped over the last week), is there anything I can do to prolong whatever is left of its life?

Im sorry, I have to say it Lol Not play any more movies????? Sorry, still pondering risk from another board. When that stuff goes it usually goes pretty quick, or at least that has been my experience.

If it's the spindle motor it's not unusual for the problem to "go away", but it will most likely come back. Temperature can be a factor which would make it intermittent. Chances are very good it won't fix itself and if it's the thrust bearing at the bottom of the motor there's no "fix" other than replacing the motor...