Re: My advice is to try to determine if the noise is external to the engine or internal....

2001 Boxster S with 102,000 miles, original IMS bearing, 5,000 mile service interval with Castrol Edge 5W40, clean oil analysis, original water pump, alternator replaced 30,000 miles ago. I have a low to mid-tone whine, it is intermittent, and occurs more frequently at start up pulling out of the garage or when slowing to a stop. I initially thought power steering pump or throw out bearing (original clutch) [I generally get 200-250K out of my factory clutches]. I have not yet driven the car with the front engine cover (behind the seats) removed to try to troubleshoot the noise. Power steering fluid is full. I slalom, but do not track the car. Current plan is a new water pump, thermostat, and IMS bearing and/or DOF at 120K and look at the clutch. Any ideas about the noise?

One way to do this is if the noise appears when the cold engine is first started and run to remove the serpentine belt and start the cold engine and listen for the noise.

If it is present, that's another post.

If it is gone then the noise is external and likely coming from an accessory drive component. Most often it is the water pump. At 102K miles the pump is closer to the end of its life than to its beginning. (The pump in my 02 lasted 172K miles. But 100K+ miles is doing pretty good.)

While you have the belt off and with the engine off check all accessory drive pulleys/shafts for any excessive (any really) free play. You have a number of accessories to check and the one with the most (any in my experience) play is the source of the noise. In the case of my 02 Boxster it was the water pump. The play wasn't obvious but it was there.

Look carefully for any leak sign under/around the water pump. Check the belt for any sharp edges. A sharp edge -- again in my Boxster's case the inner edge of the belt -- is a sign the belt is rubbing and it rubs because an accessory drive has some play and the belt mis-tracks.

While you are there check all idler roller bearings and tensioner roller bearings for any signs of excessive play or roughness. (The ones on my 02 Boxster are original at 273K miles but I had a noisy idler bearing on my 996 at under 40K miles.)

Be sure you note the direction of belt rotation and the correct routing -- draw a diagram or take a picture -- so you can install the old belt back the way it came off though if the belt is old enough replacing it with a new one wouldn't be a bad idea.

If the belt has a sharp edge you replace the accessory drive that is causing the noise and the belt.

Thanks Marc, that was exactly the kind of advice I was looking for.
Again, you da man!