'96 850R: Torque converter whine: anything to worry about?

[rhalkyard]

My automatic '96 850R has been making a faint whining noise when idling in gear when the transmission is warm. It seems to go away (or at least be drowned out by engine and road noise) when moving, and is not evident in Park or Neutral. It's too quiet to record successfully, but a brief stall test suggests that it is tied to engine speed, and it seems to come from the transmission side of the engine. As far as I can tell, this would point to the torque converter internals - in P or N, it is rotating as a unit, but while idling in gear, the turbine is stationary while the housing rotates.

The transmission fluid was flushed 3 years and 20,000 miles ago; the fluid is still a healthy red colour, and within the marks on the dipstick. The car itself is at 213,000 miles, so I realise that some things are going to be a bit worn and noisy, but automatic transmission issues do scare me somewhat. Is this a sign of impending transmission death, or is it likely to grumble away like this for years before giving any trouble?